diff --git a/addressbook/inc/class.addressbook_hooks.inc.php b/addressbook/inc/class.addressbook_hooks.inc.php
index 5e044641e4..8c564d431e 100644
--- a/addressbook/inc/class.addressbook_hooks.inc.php
+++ b/addressbook/inc/class.addressbook_hooks.inc.php
@@ -399,7 +399,7 @@ class addressbook_hooks
 	{
 		// Add users / groups this contact is shared with
 		$entry['shared_with'] = [];
-		foreach((array)$entry['shared'] as $id => $share)
+		foreach($entry['shared'] ?? [] as $share)
 		{
 			$entry['shared_with'][] = $share['shared_with'];
 		}
@@ -412,7 +412,7 @@ class addressbook_hooks
 	/**
 	 * Hook called to retrieve a app specific exportLimit
 	 *
-	 * @param array/string $location location and other parameters (not used)
+	 * @param array|string $location location and other parameters (not used)
 	 * @return the export_limit to be applied for the app, may be empty, int or string
 	 */
 	static function getAppExportLimit($location)
diff --git a/addressbook/inc/class.addressbook_zpush.inc.php b/addressbook/inc/class.addressbook_zpush.inc.php
index a2e820e360..25e2a2726e 100644
--- a/addressbook/inc/class.addressbook_zpush.inc.php
+++ b/addressbook/inc/class.addressbook_zpush.inc.php
@@ -811,16 +811,16 @@ class addressbook_zpush implements activesync_plugin_write, activesync_plugin_se
 			foreach($contacts as $contact)
 			{
 				//$item[SYNC_GAL_ALIAS] = $contact['contact_id'];
-			  	$item[SYNC_GAL_LASTNAME] = $contact['n_family']?$contact['n_family']:$contact['org_name'];
+			  	$item[SYNC_GAL_LASTNAME] = $contact['n_family'] ?? $contact['org_name'];
 			  	$item[SYNC_GAL_FIRSTNAME] = $contact['n_given'];
 				$item[SYNC_GAL_DISPLAYNAME] = $contact['n_fn'];
-				if (!trim($item[SYNC_GAL_DISPLAYNAME])) $item[SYNC_GAL_DISPLAYNAME] = $contact['n_family']?$contact['n_family']:$contact['org_name'];
-				$item[SYNC_GAL_EMAILADDRESS] = $contact['email'] ? $contact['email'] : (string)$contact['email_private'] ;
+				if (!trim($item[SYNC_GAL_DISPLAYNAME])) $item[SYNC_GAL_DISPLAYNAME] = $contact['n_family'] ?: $contact['org_name'];
+				$item[SYNC_GAL_EMAILADDRESS] = $contact['email'] ?? $contact['email_private'] ?? '';
 				//$item['nameid'] = $searchquery;
-				$item[SYNC_GAL_PHONE] = (string)$contact['tel_work'];
-				$item[SYNC_GAL_HOMEPHONE] = (string)$contact['tel_home'];
-				$item[SYNC_GAL_MOBILEPHONE] = (string)$contact['tel_cell'];
-				$item[SYNC_GAL_COMPANY] = (string)$contact['org_name'];
+				$item[SYNC_GAL_PHONE] = $contact['tel_work'] ?? '';
+				$item[SYNC_GAL_HOMEPHONE] = $contact['tel_home'] ?? '';
+				$item[SYNC_GAL_MOBILEPHONE] = $contact['tel_cell'] ?? '';
+				$item[SYNC_GAL_COMPANY] = $contact['org_name'] ?? '';
 				$item[SYNC_GAL_OFFICE] = $contact['room'];
 				$item[SYNC_GAL_TITLE ] = $contact['title'];
 
diff --git a/api/src/Auth.php b/api/src/Auth.php
index 677620297f..d7e52ab9f9 100644
--- a/api/src/Auth.php
+++ b/api/src/Auth.php
@@ -600,7 +600,7 @@ class Auth
 		foreach(self::$crypt_params as $type => $params)
 		{
 			list(,$prefix, $random, $postfix) = $params;
-			list(,$d) = explode('$', $prefix);
+			list(,$d) = explode('$', $prefix)+[null,null];
 			if ($dollar === $d || !$dollar && ($first[0] === $prefix[0] || $first[0] !== '_' && !$prefix))
 			{
 				$len = !$postfix ? strlen($prefix)+$random : strlen($prefix.$salt.$postfix);
diff --git a/api/src/Auth/Ads.php b/api/src/Auth/Ads.php
index 023700fbc4..7243fe06a9 100644
--- a/api/src/Auth/Ads.php
+++ b/api/src/Auth/Ads.php
@@ -91,7 +91,7 @@ class Ads implements Backend
 
 		if ($allValues && $allValues['count'] > 0)
 		{
-			if($GLOBALS['egw_info']['server']['case_sensitive_username'] == true)
+			if(!empty($GLOBALS['egw_info']['server']['case_sensitive_username']))
 			{
 				if($allValues[0]['samaccountname'][0] != $username)
 				{
@@ -272,4 +272,4 @@ class Ads implements Backend
 		}
 		return false;
 	}
-}
+}
\ No newline at end of file
diff --git a/api/src/Auth/Sql.php b/api/src/Auth/Sql.php
index ad55f0c385..2948e178e7 100644
--- a/api/src/Auth/Sql.php
+++ b/api/src/Auth/Sql.php
@@ -78,7 +78,7 @@ class Sql implements Backend
 				$type != $this->type && in_array($type, explode(',',strtolower($GLOBALS['egw_info']['server']['pwd_migration_types']))))
 			{
 				// do we have to migrate an old password ?
-				if($GLOBALS['egw_info']['server']['pwd_migration_allowed'] && !empty($GLOBALS['egw_info']['server']['pwd_migration_types']))
+				if (!empty($GLOBALS['egw_info']['server']['pwd_migration_allowed']) && !empty($GLOBALS['egw_info']['server']['pwd_migration_types']))
 				{
 					if (!$match)
 					{
diff --git a/api/src/Categories.php b/api/src/Categories.php
index 53adc8a654..0e6ebd1c6c 100644
--- a/api/src/Categories.php
+++ b/api/src/Categories.php
@@ -923,7 +923,7 @@ class Categories
 		{
 			return !empty($cat['data']) ? json_php_unserialize($cat['data'], true) : array();
 		}
-		elseif ($cat[$item])
+		elseif (!empty($cat[$item]))
 		{
 			return $cat[$item];
 		}
diff --git a/api/src/Contacts.php b/api/src/Contacts.php
index 8d61b8da6e..c59b72be1c 100755
--- a/api/src/Contacts.php
+++ b/api/src/Contacts.php
@@ -450,7 +450,7 @@ class Contacts extends Contacts\Storage
 	 */
 	function fileas($contact,$type=null, $isUpdate=false)
 	{
-		if (is_null($type)) $type = $contact['fileas_type'];
+		if (is_null($type)) $type = $contact['fileas_type'] ?? null;
 		if (!$type) $type = $this->prefs['fileas_default'] ? $this->prefs['fileas_default'] : $this->fileas_types[0];
 
 		if (strpos($type,'n_fn') !== false) $contact['n_fn'] = $this->fullname($contact);
@@ -909,7 +909,7 @@ class Contacts extends Contacts\Storage
 		if (!array_key_exists('photo_unchanged',$contact)) $contact['photo_unchanged'] = true;
 
 		// remember if we add or update a entry
-		if (($isUpdate = $contact['id']))
+		if (($isUpdate = $contact['id'] ?? null))
 		{
 			if (!isset($contact['owner']) || !isset($contact['private']))	// owner/private not set on update, eg. SyncML
 			{
@@ -942,10 +942,10 @@ class Contacts extends Contacts\Storage
 				$contact['owner'] = $this->default_addressbook ? $this->default_addressbook : $this->user;
 			}
 			// allow admins to import contacts with creator / created date set
-			if (!$contact['creator'] || !$ignore_acl && !$this->is_admin($contact)) $contact['creator'] = $this->user;
-			if (!$contact['created'] || !$ignore_acl && !$this->is_admin($contact)) $contact['created'] = $this->now_su;
+			if (empty($contact['creator']) || !$ignore_acl && !$this->is_admin($contact)) $contact['creator'] = $this->user;
+			if (empty($contact['created']) || !$ignore_acl && !$this->is_admin($contact)) $contact['created'] = $this->now_su;
 
-			if (!$contact['tid']) $contact['tid'] = 'n';
+			if (empty($contact['tid'])) $contact['tid'] = 'n';
 			$update_type = "add";
 		}
 		// ensure accounts and group addressbooks are never private!
@@ -964,9 +964,9 @@ class Contacts extends Contacts\Storage
 			$contact['jpegphoto'] = $this->resize_photo($contact['jpegphoto']);
 		}
 		// convert categories
-		if (is_array($contact['cat_id']))
+		if (isset($contact['cat_id']) && is_array($contact['cat_id']))
 		{
-			$contact['cat_id'] = implode(',',$contact['cat_id']);
+			$contact['cat_id'] = implode(',',$contact['cat_id']) ?: null;
 		}
 
 		// Update country codes
@@ -983,7 +983,7 @@ class Contacts extends Contacts\Storage
 					$contact[$c_prefix.'countrycode'] = null;
 				}
 			}
-			if($contact[$c_prefix.'countrycode'] != null)
+			if(isset($contact[$c_prefix.'countrycode']))
 			{
 				$contact[$c_prefix.'countryname'] = null;
 			}
@@ -1030,7 +1030,7 @@ class Contacts extends Contacts\Storage
 
 		// IF THE OLD ENTRY IS A ACCOUNT, dont allow to change the owner/location
 		// maybe we need that for id and account_id as well.
-		if (is_array($old) && (!isset($old['owner']) || empty($old['owner'])))
+		if (isset($old) && is_array($old) && (!isset($old['owner']) || empty($old['owner'])))
 		{
 			if (isset($to_write['owner']) && !empty($to_write['owner']))
 			{
@@ -1057,7 +1057,7 @@ class Contacts extends Contacts\Storage
 			}
 
 			// if contact is an account and account-relevant data got updated, handle it like account got updated
-			if ($contact['account_id'] && $isUpdate &&
+			if (!empty($contact['account_id']) && $isUpdate &&
 				($old['email'] != $contact['email'] || $old['n_family'] != $contact['n_family'] || $old['n_given'] != $contact['n_given']))
 			{
 				// invalidate the cache of the accounts class
@@ -1076,17 +1076,17 @@ class Contacts extends Contacts\Storage
 			}
 
 			// Check for restore of deleted contact, restore held links
-			if($old && $old['tid'] == self::DELETED_TYPE && $contact['tid'] != self::DELETED_TYPE)
+			if(isset($old) && $old['tid'] == self::DELETED_TYPE && $contact['tid'] != self::DELETED_TYPE)
 			{
 				Link::restore('addressbook', $contact['id']);
 			}
 
 			// Record change history for sql - doesn't work for LDAP accounts
-			$deleted = ($old['tid'] == self::DELETED_TYPE || $contact['tid'] == self::DELETED_TYPE);
-			if(!$contact['account_id'] || $contact['account_id'] && $this->account_repository == 'sql')
+			$deleted = (isset($old) && $old['tid'] == self::DELETED_TYPE || $contact['tid'] == self::DELETED_TYPE);
+			if(empty($contact['account_id']) || $contact['account_id'] && $this->account_repository == 'sql')
 			{
 				if (!isset($this->tracking)) $this->tracking = new Contacts\Tracking($this);
-				$this->tracking->track($to_write, $old ? $old : null, null, $deleted);
+				$this->tracking->track($to_write, $old ?? null, null, $deleted);
 			}
 
 			// Notify linked apps about changes in the contact data
@@ -1264,7 +1264,7 @@ class Contacts extends Contacts\Storage
 		{
 			$access = !!array_intersect($memberships,$GLOBALS['egw']->accounts->memberships($contact['account_id'],true));
 		}
-		else if ($contact['id'] && $GLOBALS['egw']->acl->check('A'.$contact['id'], $needed, 'addressbook'))
+		elseif (!empty($contact['id']) && $GLOBALS['egw']->acl->check('A'.$contact['id'], $needed, 'addressbook'))
 		{
 			$access = true;
 		}
@@ -2908,7 +2908,7 @@ class Contacts extends Contacts\Storage
 			$phoneNumberUtil->format($number, \libphonenumber\PhoneNumberFormat::INTERNATIONAL), 3);
 		$rest_without_space = preg_replace('/[^0-9]/', '', $rest);
 		/** @var Contacts\Sql */
-		$backend = $this->get_backend(null, $filter['owner']);
+		$backend = $this->get_backend(null, $filter['owner'] ?? null);
 		// SQL Backend supporting regexp_replace (MySQL 8.0+ or MariaDB 10.0+ or PostgreSQL)
 		if (is_a($backend, Contacts\Sql::class) && $this->db->regexp_replace('test', '', '') !== 'test')
 		{
diff --git a/api/src/Contacts/Sql.php b/api/src/Contacts/Sql.php
index 5647352ade..dbb2a6a8e6 100644
--- a/api/src/Contacts/Sql.php
+++ b/api/src/Contacts/Sql.php
@@ -564,7 +564,7 @@ class Sql extends Api\Storage
 					$filter[] = "($this->table_name.contact_owner=".(int)$GLOBALS['egw_info']['user']['account_id'].
 						" OR $shared_sql".
 						" OR contact_private=0 AND $this->table_name.contact_owner IN (".
-						implode(',',array_keys($this->grants)).") $groupmember_sql OR $this->table_name.contact_owner IS NULL)";
+						implode(',',array_keys($this->grants)).") ".($groupmember_sql ?? '')." OR $this->table_name.contact_owner IS NULL)";
 				}
 				else
 				{
@@ -1193,7 +1193,7 @@ class Sql extends Api\Storage
 
 		if (is_array($keys) && count($keys)) $this->data_merge($keys);
 
-		$new_entry = !$this->data['id'];
+		$new_entry = empty($this->data['id']);
 
 		if (isset($this->data['etag']))		// do we have an etag in the data to write
 		{
diff --git a/api/src/Contacts/Storage.php b/api/src/Contacts/Storage.php
index 7d651ccc64..0d6d6bd38c 100755
--- a/api/src/Contacts/Storage.php
+++ b/api/src/Contacts/Storage.php
@@ -542,9 +542,9 @@ class Storage
 	function save(&$contact)
 	{
 		// save mainfields
-		if ($contact['id'] && $this->contact_repository != $this->account_repository && is_object($this->so_accounts) &&
+		if (!empty($contact['id']) && $this->contact_repository != $this->account_repository && is_object($this->so_accounts) &&
 			($this->contact_repository == 'sql' && !is_numeric($contact['id']) ||
-			 $this->contact_repository == 'ldap' && is_numeric($contact['id'])))
+			    $this->contact_repository == 'ldap' && is_numeric($contact['id'])))
 		{
 			$this->so_accounts->data = $this->data2db($contact);
 			$error_nr = $this->so_accounts->save();
@@ -566,7 +566,7 @@ class Storage
 				$contact['id'] = $this->somain->data['id'];
 				$contact['uid'] = $this->somain->data['uid'];
 				$contact['etag'] = $this->somain->data['etag'];
-				$contact['files'] = $this->somain->data['files'];
+				$contact['files'] = $this->somain->data['files'] ?? null;
 
 				if ($this->contact_repository == 'sql-ldap')
 				{
diff --git a/api/src/Contacts/Tracking.php b/api/src/Contacts/Tracking.php
index a7435a0b1e..516de09ece 100644
--- a/api/src/Contacts/Tracking.php
+++ b/api/src/Contacts/Tracking.php
@@ -113,7 +113,7 @@ class Tracking extends Api\Storage\Tracking
 		switch($name)
 		{
 			case 'copy':
-				if ($data['is_contactform'])
+				if (!empty($data['is_contactform']))
 				{
 					$copy = preg_split('/, ?/',$data['email_contactform']);
 					if  ($data['email_copytoreceiver']) $copy[] = $data['email'];
@@ -122,7 +122,7 @@ class Tracking extends Api\Storage\Tracking
 				break;
 
 			case 'sender':
-				if ($data['is_contactform'])
+				if (!empty($data['is_contactform']))
 				{
 					return $data['email'] ? $data['n_given'].' '.$data['n_family'].' <'.$data['email'].'>' : null;
 				}
@@ -290,4 +290,4 @@ class Tracking extends Api\Storage\Tracking
 
 		return $details;
 	}
-}
+}
\ No newline at end of file
diff --git a/api/src/DateTime.php b/api/src/DateTime.php
index 1f35571272..daaf770f95 100644
--- a/api/src/DateTime.php
+++ b/api/src/DateTime.php
@@ -168,7 +168,7 @@ class DateTime extends \DateTime
 					$time['day']   = (int)substr($time['full'],6,2);
 				}
 				if (isset($time['year'])) $this->setDate((int)$time['year'],(int)$time['month'],isset($time['day']) ? (int)$time['day'] : (int)$time['mday']);
-				$this->setTime((int)$time['hour'],(int)$time['minute'],(int)$time['second']);
+				$this->setTime((int)($time['hour'] ?? 0),(int)($time['minute'] ?? 0),(int)($time['second'] ?? 0));
 				break;
 
 			case 'object':
diff --git a/api/src/Mail.php b/api/src/Mail.php
index af11f64290..320d33bd1a 100644
--- a/api/src/Mail.php
+++ b/api/src/Mail.php
@@ -1595,13 +1595,13 @@ class Mail
 				} /*else $sent_not = "";*/
 				//error_log(__METHOD__.' ('.__LINE__.') '.array2string($headerObject));
 				$headerObject['DATE'] = $headerForPrio['DATE'];
-				$headerObject['SUBJECT'] = (is_array($headerForPrio['SUBJECT'])?$headerForPrio['SUBJECT'][0]:$headerForPrio['SUBJECT']);
-				$headerObject['FROM'] = (array)($headerForPrio['FROM']?$headerForPrio['FROM']:($headerForPrio['REPLY-TO']?$headerForPrio['REPLY-TO']:$headerForPrio['RETURN-PATH']));
-				$headerObject['TO'] = (array)$headerForPrio['TO'];
+				$headerObject['SUBJECT'] = is_array($headerForPrio['SUBJECT'] ?? null) ? $headerForPrio['SUBJECT'][0] : ($headerForPrio['SUBJECT']??null);
+				$headerObject['FROM'] = (array)($headerForPrio['FROM']?:($headerForPrio['REPLY-TO']?:$headerForPrio['RETURN-PATH']));
+				$headerObject['TO'] = (array)($headerForPrio['TO'] ?? []);
 				$headerObject['CC'] = isset($headerForPrio['CC'])?(array)$headerForPrio['CC']:array();
 				$headerObject['BCC'] = isset($headerForPrio['BCC'])?(array)$headerForPrio['BCC']:array();
 				$headerObject['REPLY-TO'] = isset($headerForPrio['REPLY-TO'])?(array)$headerForPrio['REPLY-TO']:array();
-				$headerObject['PRIORITY'] = isset($headerForPrio['X-PRIORITY'])?$headerForPrio['X-PRIORITY']:null;
+				$headerObject['PRIORITY'] = $headerForPrio['X-PRIORITY']??null;
 				foreach (array('FROM','TO','CC','BCC','REPLY-TO') as $key)
 				{
 					$address = array();
diff --git a/api/src/Mail/Account.php b/api/src/Mail/Account.php
index 6d3ca4883b..e256af5a5b 100644
--- a/api/src/Mail/Account.php
+++ b/api/src/Mail/Account.php
@@ -270,7 +270,7 @@ class Account implements \ArrayAccess
 				$params += Notifications::read($params['acc_id'], $called_for ? array(0, $called_for) : $called_for);
 			}
 			if (!empty($params['acc_imap_logintype']) && empty($params['acc_imap_username']) &&
-				$GLOBALS['egw_info']['user']['account_id'] &&
+				!empty($GLOBALS['egw_info']['user']['account_id']) &&
 				(!isset($called_for) || $called_for == $GLOBALS['egw_info']['user']['account_id']))
 			{
 				// get username/password from current user, let it overwrite credentials for all/no session
@@ -291,7 +291,7 @@ class Account implements \ArrayAccess
 		unset($this->smtpServer);
 		unset($this->smtpTransport);
 
-		$this->user = $called_for ? $called_for : $GLOBALS['egw_info']['user']['account_id'];
+		$this->user = $called_for ?: $GLOBALS['egw_info']['user']['account_id'] ?? null;
 	}
 
 	public static function ssl2secure($ssl)
@@ -1491,7 +1491,7 @@ class Account implements \ArrayAccess
 		$where = array();
 		if ($only_current_user !== false)
 		{
-			$account_id = $only_current_user === true ? $GLOBALS['egw_info']['user']['account_id'] : $only_current_user;
+			$account_id = $only_current_user === true ? ($GLOBALS['egw_info']['user']['account_id']??null) : $only_current_user;
 			// no account_id happens eg. for notifications during login
 			if ($account_id && !is_numeric($account_id))
 			{
@@ -1774,7 +1774,7 @@ class Account implements \ArrayAccess
 	 */
 	protected static function memberships($user=null)
 	{
-		if (!$user) $user = $GLOBALS['egw_info']['user']['account_id'];
+		if (!$user) $user = $GLOBALS['egw_info']['user']['account_id'] ?? null;
 
 		$memberships = $GLOBALS['egw']->accounts->memberships($user, true);
 		$memberships[] = $user;
diff --git a/api/src/Mail/Credentials.php b/api/src/Mail/Credentials.php
index 102bb8dcb7..1d41e475d2 100644
--- a/api/src/Mail/Credentials.php
+++ b/api/src/Mail/Credentials.php
@@ -178,7 +178,7 @@ class Credentials
 		if (is_null($type)) $type = self::ALL;
 		if (is_null($account_id))
 		{
-			$account_id = array(0, $GLOBALS['egw_info']['user']['account_id']);
+			$account_id = array(0, $GLOBALS['egw_info']['user']['account_id'] ?? null);
 		}
 
 		// check cache, if nothing found, query database
@@ -312,7 +312,7 @@ class Credentials
 	public static function from_session(array $data, $set_identity=true)
 	{
 		// if the username contains non-ascii chars, try email address, as Dovecot does NOT deal with non-ascii usernames
-		if (is_a($data['acc_imap_type'], Api\Mail\Imap\Dovecot::class, true) &&
+		if (isset($data['acc_imap_type']) && is_a($data['acc_imap_type'], Api\Mail\Imap\Dovecot::class, true) &&
 			in_array($data['acc_imap_logintype'], ['standard', 'vmailmgr']) &&
 			preg_match('/[^\x20-\x7e]/', $GLOBALS['egw_info']['user']['account_lid']))
 		{
diff --git a/api/src/Mail/Html.php b/api/src/Mail/Html.php
index b1958a756e..21a6f9721e 100644
--- a/api/src/Mail/Html.php
+++ b/api/src/Mail/Html.php
@@ -181,7 +181,7 @@ class Html
 				if ($addbracesforendtag === false )
 				{
 					if (stripos($_body,'<'.$tag)!==false)  $ct = preg_match_all('#<'.$tag.'(?:\s.*)?>(.+)'.$endtag.'#isU', $_body, $found);
-					if ($ct>0)
+					if (isset($ct) && $ct > 0)
 					{
 						//error_log(__METHOD__.__LINE__.array2string($found[0]));
 						// only replace what we have found
diff --git a/api/src/Mail/Notifications.php b/api/src/Mail/Notifications.php
index 54b8343967..1185157001 100644
--- a/api/src/Mail/Notifications.php
+++ b/api/src/Mail/Notifications.php
@@ -56,7 +56,7 @@ class Notifications
 	{
 		if (is_null($account_id))
 		{
-			$account_id = array(0, $GLOBALS['egw_info']['user']['account_id']);
+			$account_id = array(0, $GLOBALS['egw_info']['user']['account_id'] ?? null);
 		}
 
 		// check cache, if nothing found, query database
@@ -186,4 +186,4 @@ class Notifications
 		self::$db = isset($GLOBALS['egw_setup']) ? $GLOBALS['egw_setup']->db : $GLOBALS['egw']->db;
 	}
 }
-Notifications::init_static();
+Notifications::init_static();
\ No newline at end of file
diff --git a/api/src/Session.php b/api/src/Session.php
index c309f09e9f..bb33974a40 100644
--- a/api/src/Session.php
+++ b/api/src/Session.php
@@ -1324,8 +1324,8 @@ class Session
 		$session =& $_SESSION[self::EGW_SESSION_VAR];
 
 		// we need to restore the limits and if authenticated via token
-		$this->limits = $session['session_limits'];
-		$this->token_auth = $session['session_token_auth'];
+		$this->limits = $session['session_limits'] ?? null;
+		$this->token_auth = $session['session_token_auth'] ?? null;
 
 		if ($session['session_dla'] <= time() - $GLOBALS['egw_info']['server']['sessions_timeout'])
 		{
@@ -1910,7 +1910,7 @@ class Session
 			if ($egw_path[0] != '/') $egw_path = parse_url($egw_path,PHP_URL_PATH);
 			if ($action == '/Microsoft-Server-ActiveSync')
 			{
-				$action .= '?Cmd='.$_GET['Cmd'].'&DeviceId='.$_GET['DeviceId'];
+				$action .= '?Cmd='.($_GET['Cmd']??null).'&DeviceId='.($_GET['DeviceId']??null);
 			}
 			elseif ($egw_path)
 			{
diff --git a/api/src/Translation.php b/api/src/Translation.php
index b2ee7edbb7..0a63555b2c 100644
--- a/api/src/Translation.php
+++ b/api/src/Translation.php
@@ -188,7 +188,7 @@ class Translation
 
 		if ($load_translations)
 		{
-			if ($GLOBALS['egw_info']['user']['preferences']['common']['lang'])
+			if (!empty($GLOBALS['egw_info']['user']['preferences']['common']['lang']))
 			{
 				self::$userlang = $GLOBALS['egw_info']['user']['preferences']['common']['lang'];
 			}
@@ -953,7 +953,7 @@ class Translation
 			return utf8_decode($data);
 		}
 		try {
-			if (self::$mbstring && !$prefer_iconv && ($data = @mb_convert_encoding($data, $to, $from)) != '')
+			if (self::$mbstring && empty($prefer_iconv) && ($data = @mb_convert_encoding($data, $to, $from)) != '')
 			{
 				return $data;
 			}
diff --git a/api/src/Vfs/Sqlfs/StreamWrapper.php b/api/src/Vfs/Sqlfs/StreamWrapper.php
index d6be3a4ebb..326549c9a7 100644
--- a/api/src/Vfs/Sqlfs/StreamWrapper.php
+++ b/api/src/Vfs/Sqlfs/StreamWrapper.php
@@ -1215,7 +1215,7 @@ class StreamWrapper extends Api\Db\Pdo implements Vfs\StreamWrapperIface
 		static $max_subquery_depth=null;
 		if (is_null($max_subquery_depth))
 		{
-			$max_subquery_depth = $GLOBALS['egw_info']['server']['max_subquery_depth'];
+			$max_subquery_depth = $GLOBALS['egw_info']['server']['max_subquery_depth'] ?? null;
 			if (!$max_subquery_depth) $max_subquery_depth = 7;	// setting current default of 7, if nothing set
 		}
 		if (self::LOG_LEVEL > 1) error_log(__METHOD__."('$url',$flags)");
diff --git a/api/src/loader/common.php b/api/src/loader/common.php
index eddd8cf354..749f0a285a 100755
--- a/api/src/loader/common.php
+++ b/api/src/loader/common.php
@@ -29,7 +29,7 @@ if (!function_exists('get_magic_quotes_gpc'))
 }
 
 /**
-* applies stripslashes recursivly on each element of an array
+* applies stripslashes recursively on each element of an array
 *
 * @param array &$var
 * @return array
@@ -116,7 +116,7 @@ if (!function_exists('imap_rfc822_parse_adrlist'))
 		foreach(explode(',', $address) as $part)
 		{
 			$trimmed = trim(($pending ? $pending.',' : '').$part);
-			if (($trimmed[0] == '"' && substr($trimmed, -1) != '>')||strpos($part, '@')===false)
+			if ((($trimmed[0]??null) == '"' && substr($trimmed, -1) != '>')||strpos($part, '@')===false)
 			{
 				$pending .= ($pending ? $pending.',' : '').$part;
 				continue;
@@ -366,7 +366,7 @@ function function_backtrace($remove=0)
 			{
 				$ret[] = (isset($level['class'])?$level['class'].$level['type']:'').$level['function'].
 					($n > 0 && isset($backtrace[$n-1]['line']) ? ':'.$backtrace[$n-1]['line'] : '').	// add line number of call
-					(!$level['class'] && !is_object($level['args'][0]) && $level['function'] != 'unserialize' ?
+					(empty($level['class']) && !is_object($level['args'][0]) && $level['function'] != 'unserialize' ?
 					'('.substr(str_replace(EGW_SERVER_ROOT,'',(string)$level['args'][0]),0,64).')' : '');
 			}
 		}
diff --git a/calendar/inc/class.calendar_bo.inc.php b/calendar/inc/class.calendar_bo.inc.php
index aec3aa376f..821b0ecab8 100644
--- a/calendar/inc/class.calendar_bo.inc.php
+++ b/calendar/inc/class.calendar_bo.inc.php
@@ -643,7 +643,7 @@ class calendar_bo
 		$offset = isset($params['offset']) && $params['offset'] !== false ? (int) $params['offset'] : false;
 		// socal::search() returns rejected group-invitations, as only the user not also the group is rejected
 		// as we cant remove them efficiantly in SQL, we kick them out here, but only if just one user is displayed
-		$users_in = (array)$params_in['users'];
+		$users_in = (array)($params_in['users']??[]);
 		$remove_rejected_by_user = !in_array($filter,array('all','rejected','everything')) &&
 			count($users_in) == 1 && $users_in[0] > 0 ? $users_in[0] : null;
 		//error_log(__METHOD__.'('.array2string($params_in).", $sql_filter) params[users]=".array2string($params['users']).' --> remove_rejected_by_user='.array2string($remove_rejected_by_user));
@@ -655,7 +655,7 @@ class calendar_bo
 		}
 		// date2ts(,true) converts to server time, db2data converts again to user-time
 		$events =& $this->so->search(isset($start) ? $this->date2ts($start,true) : null,isset($end) ? $this->date2ts($end,true) : null,
-			$users,$cat_id,$filter,$offset,(int)$params['num_rows'],$params,$remove_rejected_by_user);
+			$users,$cat_id,$filter,$offset,(int)($params['num_rows']??0),$params,$remove_rejected_by_user);
 
 		if (isset($params['cols']))
 		{
@@ -1091,7 +1091,7 @@ class calendar_bo
 		{
 			if (is_array($ids) || !isset(self::$cached_event['id']) || self::$cached_event['id'] != $ids ||
 				self::$cached_event_date_format != $date_format || $read_recurrence ||
-				self::$cached_event['recur_type'] != MCAL_RECUR_NONE && self::$cached_event_date != $date)
+				!empty(self::$cached_event['recur_type']) && self::$cached_event_date != $date)
 			{
 				$events = $this->so->read($ids,$date ? $this->date2ts($date,true) : 0, $read_recurrence);
 
@@ -1362,7 +1362,7 @@ class calendar_bo
 			$owner = $event['owner'];
 			$private = !$event['public'];
 		}
-		$grant = $grants[$owner];
+		$grant = $grants[$owner] ?? null;
 
 		// now any ACL rights (but invite rights!) implicate FREEBUSY rights (at least READ has to include FREEBUSY)
 		if ($grant & ~self::ACL_INVITE) $grant |= self::ACL_FREEBUSY;
diff --git a/calendar/inc/class.calendar_boupdate.inc.php b/calendar/inc/class.calendar_boupdate.inc.php
index 9b2d3c05cb..a48a29c62b 100644
--- a/calendar/inc/class.calendar_boupdate.inc.php
+++ b/calendar/inc/class.calendar_boupdate.inc.php
@@ -698,8 +698,8 @@ class calendar_boupdate extends calendar_bo
 				default:
 					if (is_array($new_event) && is_array($old_event))
 					{
-						$diff = max(abs(self::date2ts($old_event['start'])-self::date2ts($new_event['start'])),
-							abs(self::date2ts($old_event['end'])-self::date2ts($new_event['end'])));
+						$diff = max(abs(self::date2ts($old_event['start']??null)-self::date2ts($new_event['start']??null)),
+							abs(self::date2ts($old_event['end']??null)-self::date2ts($new_event['end']??null)));
 						$check = $ru == 'time_change_4h' ? 4 * 60 * 60 - 1 : 0;
 						if ($msg_type == MSG_MODIFIED && $diff > $check)
 						{
@@ -707,7 +707,7 @@ class calendar_boupdate extends calendar_bo
 						}
 					}
 				case 'add_cancel':
-					if ($msg_is_response && is_array($old_event) && ($old_event['owner'] == $userid || $role == 'CHAIR') ||
+					if ($msg_is_response && is_array($old_event) && (isset($old_event['owner']) && $old_event['owner'] == $userid || $role == 'CHAIR') ||
 						$msg_type == MSG_DELETED || $msg_type == MSG_ADDED || $msg_type == MSG_DISINVITE)
 					{
 						++$want_update;
@@ -1354,7 +1354,7 @@ class calendar_boupdate extends calendar_bo
 		$ret = $this->_send_update(MSG_ALARM, $to_notify, $event, False, $alarm['owner'], $alarm);
 
 		// create a new alarm for recuring events for the next event, if one exists
-		if ($event['recur_type'] != MCAL_RECUR_NONE && ($event = $this->read($alarm['cal_id'],$event_time_user+1)))
+		if (!empty($event['recur_type']) && ($event = $this->read($alarm['cal_id'],$event_time_user+1)))
 		{
 			$alarm['time'] = $this->date2ts($event['start']) - $alarm['offset'];
 			unset($alarm['times']);
@@ -1404,7 +1404,7 @@ class calendar_boupdate extends calendar_bo
 		$this->check_reset_statuses($event, $old_event);
 
 		// set recur-enddate/range-end to real end-date of last recurrence
-		if ($event['recur_type'] != MCAL_RECUR_NONE && $event['recur_enddate'] && $event['start'])
+		if (!empty($event['recur_type']) && $event['recur_enddate'] && $event['start'])
 		{
 			$event['recur_enddate'] = new Api\DateTime($event['recur_enddate'], calendar_timezones::DateTimeZone($event['tzid']));
 			$event['recur_enddate']->setTime(23,59,59);
@@ -1576,7 +1576,7 @@ class calendar_boupdate extends calendar_bo
 		$set_recurrences = $old_event ? abs(Api\DateTime::to($event['recur_enddate'] ?? null, 'utc') - Api\DateTime::to($old_event['recur_enddate'] ?? null, 'utc')) > 1 ||
 			count($old_event['recur_exception'] ?? []) != count($event['recur_exception'] ?? []) : false;
 		$set_recurrences_start = 0;
-		if (($cal_id = $this->so->save($event,$set_recurrences,$set_recurrences_start,0,$event['etag'])) && $set_recurrences && $event['recur_type'] != MCAL_RECUR_NONE)
+		if (($cal_id = $this->so->save($event,$set_recurrences,$set_recurrences_start,0,$event['etag'])) && $set_recurrences && !empty($event['recur_type']))
 		{
 			$save_event['id'] = $cal_id;
 			// unset participants to enforce the default stati for all added recurrences
@@ -1585,7 +1585,7 @@ class calendar_boupdate extends calendar_bo
 		}
 
 		// create links for new participants from addressbook, if configured
-		if($cal_id && $GLOBALS['egw_info']['server']['link_contacts'] && !empty($save_event['participants']))
+		if($cal_id && !empty($GLOBALS['egw_info']['server']['link_contacts']) && !empty($save_event['participants']))
 		{
 			foreach($save_event['participants'] as $uid => $status)
 			{
@@ -1941,7 +1941,7 @@ class calendar_boupdate extends calendar_bo
 			$this->send_update(MSG_DELETED, $to_notify, $event);
 		}
 
-		if (!$recur_date || $event['recur_type'] == MCAL_RECUR_NONE)
+		if (!$recur_date || empty($event['recur_type']))
 		{
 			$config = Api\Config::read('phpgwapi');
 			if ($event['deleted'])
@@ -1969,7 +1969,7 @@ class calendar_boupdate extends calendar_bo
 			}
 
 			// delete or keep (with new uid) exceptions of a recurring event
-			if ($event['recur_type'] != MCAL_RECUR_NONE)
+			if (!empty($event['recur_type']))
 			{
 				$exceptions_kept = 0;
 				foreach ($this->so->get_related($event['uid']) as $id)
@@ -2190,7 +2190,7 @@ class calendar_boupdate extends calendar_bo
 		// Repeated Events
 		$var['recur_type'] = Array(
 			'field'	=> lang('Repetition'),
-			'data'	=> ($event['recur_type'] != MCAL_RECUR_NONE) ? $this->recure2string($event) : '',
+			'data'	=> (!empty($event['recur_type'])) ? $this->recure2string($event) : '',
 		);
 		return $var;
 	}
@@ -2259,7 +2259,7 @@ class calendar_boupdate extends calendar_bo
 
 		foreach($event['alarm'] as &$alarm)
 		{
-			if($event['recur_type'] != MCAL_RECUR_NONE && $instance_date)
+			if(!empty($event['recur_type']) && $instance_date)
 			{
 				calendar_so::shift_alarm($event, $alarm, $instance_date);
 			}
@@ -2425,7 +2425,7 @@ class calendar_boupdate extends calendar_bo
 		}
 		elseif ($filter == 'exact')
 		{
-			if ($event['recur_type'] != MCAL_RECUR_NONE)
+			if (!empty($event['recur_type']))
 			{
 				$query[] = 'recur_type='.$event['recur_type'];
 			}
@@ -2450,7 +2450,7 @@ class calendar_boupdate extends calendar_bo
 					error_log(__FILE__.'['.__LINE__.'] '.__METHOD__.
 						'()[FOUND]:' . array2string($egwEvent)."\n",3,$this->logfile);
 				}
-				if ($egwEvent['recur_type'] != MCAL_RECUR_NONE &&
+				if (!empty($egwEvent['recur_type']) &&
 					(empty($event['uid']) || $event['uid'] == $egwEvent['uid']))
 				{
 					if ($filter == 'master')
@@ -2461,7 +2461,7 @@ class calendar_boupdate extends calendar_bo
 					{
 						$matchingEvents[] = $egwEvent['id']; // we found the event
 					}
-					elseif ($event['recur_type'] == MCAL_RECUR_NONE &&
+					elseif (empty($event['recur_type']) &&
 								$event['recurrence'] != 0)
 					{
 						$exceptions = $this->so->get_recurrence_exceptions($egwEvent, $event['tzid']);
@@ -2658,14 +2658,14 @@ class calendar_boupdate extends calendar_bo
 						$egwstart->setTimezone(self::$tz_cache[$egwEvent['tzid']]);
 						$dtstart = new Api\DateTime($event['start'], Api\DateTime::$server_timezone);
 						$dtstart->setTimezone(self::$tz_cache[$event['tzid']]);
-						if ($egwEvent['recur_type'] == MCAL_RECUR_NONE &&
-							$event['recur_type'] == MCAL_RECUR_NONE ||
-								$egwEvent['recur_type'] != MCAL_RECUR_NONE &&
-									$event['recur_type'] != MCAL_RECUR_NONE)
+						if (empty($egwEvent['recur_type']) &&
+							empty($event['recur_type']) ||
+								!empty($egwEvent['recur_type']) &&
+									!empty($event['recur_type']))
 						{
-							if ($egwEvent['recur_type'] == MCAL_RECUR_NONE &&
+							if (empty(egwEvent['recur_type']) &&
 								$egwstart->format('Ymd') == $dtstart->format('Ymd') ||
-									$egwEvent['recur_type'] != MCAL_RECUR_NONE)
+									!empty($egwEvent['recur_type']))
 							{
 								// We found an exact match
 								$matchingEvents = array($egwEvent['id']);
@@ -2684,8 +2684,8 @@ class calendar_boupdate extends calendar_bo
 						$matchingEvents = array($egwEvent['id']);
 						break;
 					}
-					if ($egwEvent['recur_type'] != MCAL_RECUR_NONE &&
-						$event['recur_type'] == MCAL_RECUR_NONE &&
+					if (!empty($egwEvent['recur_type']) &&
+						empty($event['recur_type']) &&
 							!$egwEvent['recurrence'] && $event['recurrence'])
 					{
 						$exceptions = $this->so->get_recurrence_exceptions($egwEvent, $event['tzid']);
@@ -2825,9 +2825,9 @@ class calendar_boupdate extends calendar_bo
 				}
 			}
 
-			if ($event['recur_type'] == MCAL_RECUR_NONE)
+			if (empty($event['recur_type']))
 			{
-				if ($egwEvent['recur_type'] != MCAL_RECUR_NONE)
+				if (!empty($egwEvent['recur_type']))
 				{
 					// We found a pseudo Exception
 					$pseudos[] = $egwEvent['id'] . ':' . $event['start'];
@@ -2964,7 +2964,7 @@ class calendar_boupdate extends calendar_bo
 			}
 		}
 
-		if ($event['recur_type'] != MCAL_RECUR_NONE)
+		if (!empty($event['recur_type']))
 		{
 			$type = 'SERIES-MASTER';
 		}
diff --git a/calendar/inc/class.calendar_rrule.inc.php b/calendar/inc/class.calendar_rrule.inc.php
index cc6eedfa34..df282f846f 100644
--- a/calendar/inc/class.calendar_rrule.inc.php
+++ b/calendar/inc/class.calendar_rrule.inc.php
@@ -844,7 +844,7 @@ class calendar_rrule implements Iterator
 			$end = is_a($event['end'],'DateTime') ? clone $event['end'] : new Api\DateTime($event['end'],$timestamp_tz);
 			$end->setTimezone($enddate->getTimezone());
 			$enddate->setTime($end->format('H'),$end->format('i'),0);
-			if($event['whole_day'])
+			if(!empty($event['whole_day']))
 			{
 				$enddate->setTime(23,59,59);
 			}
@@ -856,7 +856,7 @@ class calendar_rrule implements Iterator
 				$exceptions[] = is_a($exception,'DateTime') ? $exception : new Api\DateTime($exception,$timestamp_tz);
 			}
 		}
-		return new calendar_rrule($time,$event['recur_type'],$event['recur_interval'],$enddate,$event['recur_data'],$exceptions);
+		return new calendar_rrule($time,$event['recur_type'],$event['recur_interval'],$enddate??null,$event['recur_data'],$exceptions??null);
 	}
 
 	/**
diff --git a/calendar/inc/class.calendar_so.inc.php b/calendar/inc/class.calendar_so.inc.php
index 4f3b35e44b..d72cb8ed51 100644
--- a/calendar/inc/class.calendar_so.inc.php
+++ b/calendar/inc/class.calendar_so.inc.php
@@ -159,7 +159,7 @@ class calendar_so
 	 */
 	protected function cal_range_view($start, $end, array $_where=null, $deleted=false)
 	{
-		if ($GLOBALS['egw_info']['server']['no_timerange_views'] || !$start)	// using view without start-date is slower!
+		if (!empty($GLOBALS['egw_info']['server']['no_timerange_views']) || !$start)	// using view without start-date is slower!
 		{
 			return $this->cal_table;	// no need / use for a view
 		}
@@ -424,7 +424,7 @@ class calendar_so
 				$this->db->update($this->cal_table, array('cal_uid' => $event['uid']),
 					array('cal_id' => $event['id']),__LINE__,__FILE__,'calendar');
 			}
-			if (!(int)$recur_date && $event['recur_type'] != MCAL_RECUR_NONE)
+			if (!(int)$recur_date && !empty($event['recur_type']))
 			{
 				foreach($this->db->select($this->dates_table, 'cal_id,cal_start', array(
 					'cal_id' => $ids,
@@ -436,7 +436,7 @@ class calendar_so
 				break;	// as above select read all exceptions (and I dont think too short uid problem still exists)
 			}
 			// make sure we fetch only real exceptions (deleted occurrences of a series should not show up)
-			if (($recur_date &&	$event['recur_type'] != MCAL_RECUR_NONE))
+			if (($recur_date &&	!empty($event['recur_type'])))
 			{
 				//_debug_array(__METHOD__.__LINE__.' recur_date:'.$recur_date.' check cal_start:'.$event['start']);
 				foreach($this->db->select($this->dates_table, 'cal_id,cal_start', array(
@@ -468,7 +468,7 @@ class calendar_so
 		}
 
 		// check if we have a real recurance, if not set $recur_date=0
-		if (is_array($ids) || $events[(int)$ids]['recur_type'] == MCAL_RECUR_NONE)
+		if (is_array($ids) || empty($events[(int)$ids]['recur_type']))
 		{
 			$recur_date = 0;
 		}
@@ -955,7 +955,7 @@ class calendar_so
 
 		$u_join = "JOIN $this->user_table ON $this->cal_table.cal_id=$this->user_table.cal_id ".
 			"LEFT JOIN $this->repeats_table ON $this->cal_table.cal_id=$this->repeats_table.cal_id ".
-			$rejected_by_user_join;
+			($rejected_by_user_join??'');
 		// dates table join only needed to enum recuring events, we use a time-range limited view here too
 		if ($params['enum_recuring'])
 		{
@@ -1217,7 +1217,7 @@ class calendar_so
 			{
 				foreach($alarms as $id => $alarm)
 				{
-					$event_start = $alarm['time'] + $alarm['offset'];
+					$event_start = $alarm['time'] + ($alarm['offset']??0);
 
 					if (isset($events[$cal_id]))	// none recuring event
 					{
@@ -1453,9 +1453,9 @@ ORDER BY cal_user_type, cal_usre_id
 
 		$cal_id = (int)($event['id'] ?? 0);
 		unset($event['id']);
-		$set_recurrences = $set_recurrences || !$cal_id && $event['recur_type'] != MCAL_RECUR_NONE;
+		$set_recurrences = $set_recurrences || !$cal_id && !empty($event['recur_type']);
 
-		if ($event['recur_type'] != MCAL_RECUR_NONE &&
+		if (!empty($event['recur_type']) &&
 			!(int)$event['recur_interval'])
 		{
 			$event['recur_interval'] = 1;
@@ -1474,7 +1474,7 @@ ORDER BY cal_user_type, cal_usre_id
 		if (isset($event['cal_start'])) $event['range_start'] = $event['cal_start'];
 		if (isset($event['cal_end']))
 		{
-			$event['range_end'] = $event['recur_type'] == MCAL_RECUR_NONE ? $event['cal_end'] :
+			$event['range_end'] = empty($event['recur_type']) ? $event['cal_end'] :
 				($event['recur_enddate'] ? $event['recur_enddate'] : null);
 		}
 		// ensure that we find matching entries later on
@@ -1492,12 +1492,12 @@ ORDER BY cal_user_type, cal_usre_id
 		$event['cal_category'] = implode(',',$categories);
 
 		// make sure recurring events never reference to an other recurrent event
-		if ($event['recur_type'] != MCAL_RECUR_NONE) $event['cal_reference'] = 0;
+		if (!empty($event['recur_type'])) $event['cal_reference'] = 0;
 
 		if ($cal_id)
 		{
 			// query old recurrance information, before updating main table, where recur_endate is now stored
-			if ($event['recur_type'] != MCAL_RECUR_NONE)
+			if (!empty($event['recur_type']))
 			{
 				$old_repeats = $this->db->select($this->repeats_table, "$this->repeats_table.*,range_end AS recur_enddate",
 					"$this->repeats_table.cal_id=".(int)$cal_id, __LINE__, __FILE__,
@@ -1505,7 +1505,7 @@ ORDER BY cal_user_type, cal_usre_id
 			}
 			$where = array('cal_id' => $cal_id);
 			// read only timezone id, to check if it is changed
-			if ($event['recur_type'] != MCAL_RECUR_NONE)
+			if (!empty($event['recur_type']))
 			{
 				$old_tz_id = $this->db->select($this->cal_table,'tz_id',$where,__LINE__,__FILE__,'calendar')->fetchColumn();
 			}
@@ -1552,7 +1552,7 @@ ORDER BY cal_user_type, cal_usre_id
 			$this->db->update($this->cal_table, $update, array('cal_id' => $cal_id),__LINE__,__FILE__,'calendar');
 		}
 
-		if ($event['recur_type'] == MCAL_RECUR_NONE)
+		if (empty($event['recur_type']))
 		{
 			$this->db->delete($this->dates_table,array(
 				'cal_id' => $cal_id),
@@ -1764,7 +1764,7 @@ ORDER BY cal_user_type, cal_usre_id
 			}
 		}
 		// updating or saving the alarms; new alarms have a temporary numeric id!
-		if (is_array($event['alarm']))
+		if (!empty($event['alarm']) && is_array($event['alarm']))
 		{
 			foreach ($event['alarm'] as $id => $alarm)
 			{
@@ -1812,7 +1812,7 @@ ORDER BY cal_user_type, cal_usre_id
 	 */
 	public static function shift_alarm(array $_event, array &$alarm, $timestamp=null)
 	{
-		if ($_event['recur_type'] == MCAL_RECUR_NONE)
+		if (empty($_event['recur_type']))
 		{
 			return false;
 		}
@@ -2747,7 +2747,7 @@ ORDER BY cal_user_type, cal_usre_id
 		$cal_id = (int) $event['id'];
 		//error_log(__FILE__.'['.__LINE__.'] '.__METHOD__.
 		//		"($cal_id, $tz_id, $filter): " . $event['tzid']);
-		if (!$cal_id || $event['recur_type'] == MCAL_RECUR_NONE) return false;
+		if (!$cal_id || empty($event['recur_type'])) return false;
 
 		$days = array();
 
diff --git a/calendar/inc/class.calendar_tracking.inc.php b/calendar/inc/class.calendar_tracking.inc.php
index ecab598a28..2a83a203ec 100644
--- a/calendar/inc/class.calendar_tracking.inc.php
+++ b/calendar/inc/class.calendar_tracking.inc.php
@@ -125,7 +125,7 @@ class calendar_tracking extends Api\Storage\Tracking
 	{
 		// Don't try to track dates on recurring events.
 		// It won't change for the base event, and any change to the time creates an exception
-		if($data['recur_type'])
+		if(!empty($data['recur_type']))
 		{
 			unset($data['start']); unset($data['end']);
 			unset($old['start']); unset($old['end']);
diff --git a/calendar/inc/class.calendar_zpush.inc.php b/calendar/inc/class.calendar_zpush.inc.php
index b143bdc4b2..a4d92dfab5 100644
--- a/calendar/inc/class.calendar_zpush.inc.php
+++ b/calendar/inc/class.calendar_zpush.inc.php
@@ -187,7 +187,7 @@ class calendar_zpush implements activesync_plugin_write, activesync_plugin_meeti
 		$type = $user = null;
 		$this->backend->splitID($id,$type,$user);
 
-		if (!$cutoffdate) $cutoffdate = $this->bo->now - 100*24*3600;	// default three month back -30 breaks all sync recurrences
+		if (!$cutoffdate) $cutoffdate = time() - 100*24*3600;	// default three month back -30 breaks all sync recurrences
 
 		$filter = array(
 			'users' => $user,
@@ -783,7 +783,7 @@ class calendar_zpush implements activesync_plugin_write, activesync_plugin_meeti
 		}
 		// preserve all resource types not account, contact or email (eg. resources) for existing events
 		// $account is also preserved, as AS does not add him as participant!
-		foreach((array)$event['participant_types'] as $type => $parts)
+		foreach($event['participant_types'] ?? [] as $type => $parts)
 		{
 			if (in_array($type,array('c','e'))) continue;	// they are correctly representable in AS
 
@@ -800,10 +800,10 @@ class calendar_zpush implements activesync_plugin_write, activesync_plugin_meeti
 			}
 		}
 		// add calendar owner as participant, as otherwise event will NOT be in his calendar, in which it was posted
-		if (!$event['id'] || !$participants || !isset($participants[$account]))
+		if (empty($event['id']) || !$participants || !isset($participants[$account]))
 		{
 			$participants[$account] = calendar_so::combine_status($account == $GLOBALS['egw_info']['user']['account_id'] ?
-				'A' : 'U',1,!$chair_set ? 'CHAIR' : 'REQ-PARTICIPANT');
+				'A' : 'U',1,empty($chair_set) ? 'CHAIR' : 'REQ-PARTICIPANT');
 		}
 		$event['participants'] = $participants;
 
@@ -1138,12 +1138,12 @@ class calendar_zpush implements activesync_plugin_write, activesync_plugin_meeti
 
 				if (!$info) continue;
 
-				if (!$info['email'] && $info['responsible'])
+				if (empty($info['email']) && !empty($info['responsible']))
 				{
 					$info['email'] = $GLOBALS['egw']->accounts->id2name($info['responsible'], 'account_email', true);
 				}
 				$attendee->name = empty($info['cn']) ? $info['name'] : $info['cn'];
-				$attendee->email = $info['email'];
+				$attendee->email = $info['email'] ?? null;
 
 				// external organizer: make him AS organizer, to get correct notifications
 				if ($role == 'CHAIR' && $uid[0] == 'e' && !empty($attendee->email))
diff --git a/infolog/inc/class.infolog_hooks.inc.php b/infolog/inc/class.infolog_hooks.inc.php
index 3d58204cac..4ac74653cf 100644
--- a/infolog/inc/class.infolog_hooks.inc.php
+++ b/infolog/inc/class.infolog_hooks.inc.php
@@ -61,7 +61,7 @@ class infolog_hooks
 			 ),
 			'add' => array(
 				'menuaction' => 'infolog.infolog_ui.edit',
-				'type'   => $GLOBALS['egw_info']['user']['preferences']['preferred_type']
+				'type'   => $GLOBALS['egw_info']['user']['preferences']['preferred_type'] ?? '',
 			),
 			'add_app'    => 'action',
 			'add_id'     => 'action_id',
diff --git a/infolog/inc/class.infolog_so.inc.php b/infolog/inc/class.infolog_so.inc.php
index 9a5edbe758..168cbd83c2 100644
--- a/infolog/inc/class.infolog_so.inc.php
+++ b/infolog/inc/class.infolog_so.inc.php
@@ -306,7 +306,7 @@ class infolog_so
 	{
 		$vars = null;
 		preg_match('/(done|open|offer|deleted|\+deleted)/',$_filter,$vars);
-		$filter = $vars[1];
+		$filter = $vars[1]??null;
 
 		switch ($filter)
 		{
@@ -335,7 +335,7 @@ class infolog_so
 	{
 		$vars = null;
 		preg_match('/(open-upcoming|upcoming|today|overdue|date|enddate)([-\\/.0-9]*)/',$_filter,$vars);
-		$filter = $vars[1];
+		$filter = $vars[1]??null;
 
 		if (isset($vars[2]) && !empty($vars[2]) && ($date = preg_split('/[-\\/.]/',$vars[2])))
 		{
@@ -866,7 +866,7 @@ class infolog_so
 					continue;
 				}
 				if ($col[0] != '#' && substr($col,0,5) != 'info_' && isset($table_def['fd']['info_'.$col])) $col = 'info_'.$col;
-				if ((string)$data !== '' && preg_match('/^[a-z_0-9]+$/i',$col))
+				if ((!empty($data) || (string)$data !== '') && preg_match('/^[a-z_0-9]+$/i',$col))
 				{
 					switch ($col)
 					{
@@ -1034,12 +1034,12 @@ class infolog_so
 			if (is_null($index_load_cfs) && !empty($query['col_filter']['info_type']))
 			{
 				$config_data = Api\Config::read('infolog');
-				$index_load_cfs = $config_data['index_load_cfs'];
+				$index_load_cfs = $config_data['index_load_cfs'] ?? [];
 				if (!is_array($index_load_cfs)) $index_load_cfs = explode(',', $index_load_cfs);
 			}
 			// if no specific custom field is selected, show/query all custom fields
-			if ($ids && ($query['custom_fields'] || $query['csv_export'] ||
-				$index_load_cfs && $query['col_filter']['info_type'] && in_array($query['col_filter']['info_type'],$index_load_cfs)))
+			if ($ids && (!empty($query['custom_fields']) || !empty($query['csv_export']) ||
+				$index_load_cfs && !empty($query['col_filter']['info_type']) && in_array($query['col_filter']['info_type'],$index_load_cfs)))
 			{
 				$where = array('info_id' => array_keys($ids));
 				if (!($query['csv_export'] || strchr(is_array($query['selectcols']) ? implode(',',$query['selectcols']):$query['selectcols'],'#') === false ||
diff --git a/infolog/inc/class.infolog_zpush.inc.php b/infolog/inc/class.infolog_zpush.inc.php
index c7d8dd4384..ec473650fd 100644
--- a/infolog/inc/class.infolog_zpush.inc.php
+++ b/infolog/inc/class.infolog_zpush.inc.php
@@ -242,7 +242,7 @@ class infolog_zpush implements activesync_plugin_write
 		$mimesupport = $contentparameters->GetMimeSupport();
 		$bodypreference = $contentparameters->GetBodyPreference(); /* fmbiete's contribution r1528, ZP-320 */
 
-		ZLog::Write(LOGLEVEL_DEBUG, __METHOD__."('$folderid', $id, truncsize=$truncsize, bodyprefence=$bodypreference, mimesupport=$mimesupport)");
+		ZLog::Write(LOGLEVEL_DEBUG, __METHOD__."('$folderid', $id, truncsize=$truncsize, bodyprefence=".json_encode($bodypreference).", mimesupport=$mimesupport)");
 		$type = $account = null;
 		$this->backend->splitID($folderid, $type, $account);
 		if ($type != 'infolog' || !($infolog = $this->infolog->read($id, true, 'server')))
@@ -625,4 +625,4 @@ class infolog_zpush implements activesync_plugin_write
 
 		return $settings;
 	}
-}
+}
\ No newline at end of file
diff --git a/mail/inc/class.mail_zpush.inc.php b/mail/inc/class.mail_zpush.inc.php
index d0d9dcd5b2..c25907a95c 100644
--- a/mail/inc/class.mail_zpush.inc.php
+++ b/mail/inc/class.mail_zpush.inc.php
@@ -424,9 +424,9 @@ class mail_zpush implements activesync_plugin_write, activesync_plugin_sendmail,
 		{
 			$disableRuler = true;
 		}
-		$beforePlain = $beforeHtml = "";
-		$beforeHtml = ($disableRuler ?'&nbsp;<br>':'&nbsp;<br><hr style="border:dotted 1px silver; width:90%; border:dotted 1px silver;">');
-		$beforePlain = ($disableRuler ?"\r\n\r\n":"\r\n\r\n-- \r\n");
+
+		$beforeHtml = !empty($disableRuler) ? '&nbsp;<br>' : '&nbsp;<br><hr style="border:dotted 1px silver; width:90%; border:dotted 1px silver;">';
+		$beforePlain = !empty($disableRuler) ?"\r\n\r\n" : "\r\n\r\n-- \r\n";
 		$sigText = Mail::merge($signature,array($GLOBALS['egw']->accounts->id2name($GLOBALS['egw_info']['user']['account_id'],'person_id')));
 		if ($this->debugLevel>0) ZLog::Write(LOGLEVEL_DEBUG,__METHOD__.__LINE__.' Signature to use:'.$sigText);
 		$sigTextHtml = $beforeHtml.$sigText;
@@ -553,9 +553,9 @@ class mail_zpush implements activesync_plugin_write, activesync_plugin_sendmail,
 				$emailAddress = $addressObject->mailbox. ($addressObject->host ? '@'.$addressObject->host : '');
 				if ($ClientSideMeetingRequest === true && $allowSendingInvitations == 'sendifnocalnotif' &&
 					calendar_boupdate::email_update_requested($emailAddress, isset($cSMRMethod) ? $cSMRMethod : 'REQUEST',
-						$organizer && !strcasecmp($emailAddress, $organizer) ? 'CHAIR' : ''))
+						!empty($organizer) && !strcasecmp($emailAddress, $organizer) ? 'CHAIR' : ''))
 				{
-					ZLog::Write(LOGLEVEL_DEBUG,__METHOD__."(".__LINE__.") skiping mail to organizer '$organizer', as it will be send by calendar app");
+					ZLog::Write(LOGLEVEL_DEBUG,__METHOD__."(".__LINE__.") skiping mail to organizer ".json_encode($organizer??null).", as it will be send by calendar app");
 					continue;
 				}
 				$mailObject->AddAddress($emailAddress, $addressObject->personal);
@@ -563,7 +563,7 @@ class mail_zpush implements activesync_plugin_write, activesync_plugin_sendmail,
 			}
 		}
 		$ccCount = 0;
-		foreach((array)$ccMailAddr as $address) {
+		foreach($ccMailAddr ?? [] as $address) {
 			foreach(Mail::parseAddressList((function_exists('get_magic_quotes_gpc') && get_magic_quotes_gpc()?stripslashes($address):$address)) as $addressObject) {
 				$emailAddress = $addressObject->mailbox. ($addressObject->host ? '@'.$addressObject->host : '');
 				if ($ClientSideMeetingRequest === true && $allowSendingInvitations == 'sendifnocalnotif' && calendar_boupdate::email_update_requested($emailAddress)) continue;
@@ -572,7 +572,7 @@ class mail_zpush implements activesync_plugin_write, activesync_plugin_sendmail,
 			}
 		}
 		$bccCount = 0;
-		foreach((array)$bccMailAddr as $address) {
+		foreach($bccMailAddr ?? [] as $address) {
 			foreach(Mail::parseAddressList((function_exists('get_magic_quotes_gpc') && get_magic_quotes_gpc()?stripslashes($address):$address)) as $addressObject) {
 				$emailAddress = $addressObject->mailbox. ($addressObject->host ? '@'.$addressObject->host : '');
 				if ($ClientSideMeetingRequest === true && $allowSendingInvitations == 'sendifnocalnotif' && calendar_boupdate::email_update_requested($emailAddress)) continue;
@@ -583,7 +583,7 @@ class mail_zpush implements activesync_plugin_write, activesync_plugin_sendmail,
 		// typical organizer reply will end here with nothing send --> return true, because we suppressed the send above
 		if ($toCount+$ccCount+$bccCount == 0)
 		{
-			return $ClientSideMeetingRequest && $allowSendingInvitations === 'sendifnocalnotif' && $organizer ? true : 0; // noone to send mail to
+			return $ClientSideMeetingRequest && $allowSendingInvitations === 'sendifnocalnotif' && !empty($organizer) ? true : 0; // noone to send mail to
 		}
 		if ($ClientSideMeetingRequest === true && $allowSendingInvitations===false) return true;
 		// as we use our mailer (horde mailer) it is detecting / setting the mimetype by itself while creating the mail
@@ -797,7 +797,7 @@ class mail_zpush implements activesync_plugin_write, activesync_plugin_sendmail,
 				$asf = true;
 			}
 			if (count($folderArray) > 0) {
-				foreach((array)$bccMailAddr as $address) {
+				foreach($bccMailAddr ?? [] as $address) {
 					foreach(Mail::parseAddressList((function_exists('get_magic_quotes_gpc') && get_magic_quotes_gpc()?stripslashes($address):$address)) as $addressObject) {
 						$emailAddress = $addressObject->mailbox. ($addressObject->host ? '@'.$addressObject->host : '');
 						$mailAddr[] = array($emailAddress, $addressObject->personal);
@@ -1086,7 +1086,7 @@ class mail_zpush implements activesync_plugin_write, activesync_plugin_sendmail,
 			$output->importance = $headers['priority'] > 3 ? 0 :
 				($headers['priority'] < 3 ? 2 : 1) ;
 			$output->datereceived = $this->mail->_strtotime($headers['date'], 'ts', false);  // false = servertime
-			$output->to = $headers['to_address'];
+			$output->to = $headers['to_address'] ?? null;
 			if (!empty($headers['to'])) $output->displayto = $headers['to_address']; //$headers['FETCHED_HEADER']['to_name']
 			$output->from = $headers['sender_address'];
 			if (!empty($headers['cc_addresses'])) $output->cc = $headers['cc_addresses'];