diff --git a/addressbook/inc/class.addressbook_hooks.inc.php b/addressbook/inc/class.addressbook_hooks.inc.php
index 9a59821007..426454100b 100644
--- a/addressbook/inc/class.addressbook_hooks.inc.php
+++ b/addressbook/inc/class.addressbook_hooks.inc.php
@@ -419,11 +419,11 @@ class addressbook_hooks
 	{
 		unset($location);	// not used, but required by function signature
 
-		return $GLOBALS['egw_info']['server']['contact_export_limit'];
+		return $GLOBALS['egw_info']['server']['contact_export_limit'] ?? null;
 	}
 
 	/**
-	 * Register contacts as calendar resources (items which can be sheduled by the calendar)
+	 * Register contacts as calendar resources (items which can be scheduled by the calendar)
 	 *
 	 * @param array $args hook-params (not used)
 	 * @return array
@@ -433,7 +433,7 @@ class addressbook_hooks
 		unset($args);	// not used, but required by function signature
 
 		return array(
-			'type' => 'c',// one char type-identifiy for this resources
+			'type' => 'c',// one char type-identifier for this resource
 			'info' => 'api.EGroupware\\Api\\Contacts.calendar_info',// info method, returns array with id, type & name for a given id
 		);
 	}
@@ -633,4 +633,4 @@ class addressbook_hooks
 			]
 		];
 	}
-}
+}
\ No newline at end of file
diff --git a/addressbook/inc/class.addressbook_zpush.inc.php b/addressbook/inc/class.addressbook_zpush.inc.php
index 879e074d1e..26611048d6 100644
--- a/addressbook/inc/class.addressbook_zpush.inc.php
+++ b/addressbook/inc/class.addressbook_zpush.inc.php
@@ -129,7 +129,7 @@ class addressbook_zpush implements activesync_plugin_write, activesync_plugin_se
 
 		if (!isset($abs) || !$return_all_in_one)
 		{
-			if ($return_all_in_one && $GLOBALS['egw_info']['user']['preferences']['activesync']['addressbook-all-in-one'])
+			if ($return_all_in_one && ($GLOBALS['egw_info']['user']['preferences']['activesync']['addressbook-all-in-one'] ?? null))
 			{
 				$abs = array(
 					$GLOBALS['egw_info']['user']['account_id'] => lang('All'),
@@ -141,7 +141,7 @@ class addressbook_zpush implements activesync_plugin_write, activesync_plugin_se
 
 				if (!isset($this->addressbook)) $this->addressbook = new Api\Contacts();
 
-				$pref_abs = $GLOBALS['egw_info']['user']['preferences']['activesync']['addressbook-abs'];
+				$pref_abs = $GLOBALS['egw_info']['user']['preferences']['activesync']['addressbook-abs'] ?? [];
 				if (!is_array($pref_abs))
 				{
 					$pref_abs = $pref_abs ? explode(',',$pref_abs) : [];
@@ -917,4 +917,4 @@ class addressbook_zpush implements activesync_plugin_write, activesync_plugin_se
 		);
 		return $settings;
 	}
-}
+}
\ No newline at end of file
diff --git a/calendar/inc/class.calendar_bo.inc.php b/calendar/inc/class.calendar_bo.inc.php
index cfe6626d28..b0bf5717a3 100644
--- a/calendar/inc/class.calendar_bo.inc.php
+++ b/calendar/inc/class.calendar_bo.inc.php
@@ -262,7 +262,7 @@ class calendar_bo
 		//error_log(__METHOD__ . " registered resources=". array2string($this->resources));
 
 		$this->config = Api\Config::read('calendar');	// only used for horizont, regular calendar config is under phpgwapi
-		$this->require_acl_invite = $GLOBALS['egw_info']['server']['require_acl_invite'];
+		$this->require_acl_invite = $GLOBALS['egw_info']['server']['require_acl_invite'] ?? null;
 
 		$this->categories = new Api\Categories($this->user,'calendar');
 
@@ -1686,7 +1686,7 @@ class calendar_bo
 				$id2email[$id] = $GLOBALS['egw']->accounts->id2name($id,'account_email');
 			}
 		}
-		return $id2lid[$id].(($append_email || $id[0] == 'e') && $id2email[$id] ? ' <'.$id2email[$id].'>' : '');
+		return $id2lid[$id].(($append_email || $id[0] == 'e') && !empty($id2email[$id]) ? ' <'.$id2email[$id].'>' : '');
 	}
 
 	/**
@@ -2291,4 +2291,4 @@ class calendar_bo
 		}
 		return $set;
 	}
-}
+}
\ No newline at end of file
diff --git a/calendar/inc/class.calendar_boupdate.inc.php b/calendar/inc/class.calendar_boupdate.inc.php
index b8302a077a..d59ab6d3e2 100644
--- a/calendar/inc/class.calendar_boupdate.inc.php
+++ b/calendar/inc/class.calendar_boupdate.inc.php
@@ -833,7 +833,7 @@ class calendar_boupdate extends calendar_bo
 			$msg = $prefs['notifyAdded'];	// use a default
 		}
 		//error_log(__METHOD__."($msg_type) action='$action', $msg='$msg' returning '$method'");
-		return $method;
+		return $method ?? null;
 	}
 
 	/**
@@ -994,7 +994,7 @@ class calendar_boupdate extends calendar_bo
 					//$cleared_event = $this->read($event['id'], null, true, 'server');
 					$this->clear_private_infos($cleared_event, array($userid));
 				}
-				$userid = $res_info['responsible'];
+				$userid = $res_info['responsible'] ?? null;
 
 				if (empty($userid))	// no resource responsible: $userid===0
 				{
@@ -1247,7 +1247,7 @@ class calendar_boupdate extends calendar_bo
 						$notification->set_popupmessage($subject."\n\n".$notify_body."\n\n".$details['description']."\n\n".$details_body."\n\n");
 						$notification->set_popuplinks(array($details['link_arr']+array('app'=>'calendar')));
 
-						if(is_array($attachment)) { $notification->set_attachments(array($attachment)); }
+						if(!empty($attachment)) { $notification->set_attachments(array($attachment)); }
 						$notification->send();
 						$errors = notifications::errors(true);
 					}
@@ -1289,7 +1289,7 @@ class calendar_boupdate extends calendar_bo
 			Api\Translation::init();
 		}
 		// restore timezone, in case we had to reset it to server-timezone
-		if ($restore_tz) date_default_timezone_set($restore_tz);
+		if (!empty($restore_tz)) date_default_timezone_set($restore_tz);
 
 		return true;
 	}
@@ -2131,7 +2131,7 @@ class calendar_boupdate extends calendar_bo
 
 		$var['updated'] = Array(
 			'field'	=> lang('Updated'),
-			'data'	=> $this->format_date($event['modtime']).', '.Api\Accounts::username($event['modifier'])
+			'data'	=> $this->format_date($event['modtime'] ?? null).', '.Api\Accounts::username($event['modifier'])
 		);
 
 		$var['access'] = Array(
diff --git a/calendar/inc/class.calendar_so.inc.php b/calendar/inc/class.calendar_so.inc.php
index 7959b51ed5..bab1cecedb 100644
--- a/calendar/inc/class.calendar_so.inc.php
+++ b/calendar/inc/class.calendar_so.inc.php
@@ -50,9 +50,9 @@ define('TENTATIVE',2);
 define('ACCEPTED',3);
 define('DELEGATED',4);
 
-define('HOUR_s',60*60);
-define('DAY_s',24*HOUR_s);
-define('WEEK_s',7*DAY_s);
+if (!defined('HOUR_s')) define('HOUR_s',60*60);
+if (!defined('DAY_s'))  define('DAY_s',24*HOUR_s);
+if (!defined('WEEK_s')) define('WEEK_s',7*DAY_s);
 
 /**
  * Class to store all calendar data (storage object)
@@ -3087,4 +3087,4 @@ ORDER BY cal_user_type, cal_usre_id
 			}
 		}
 	}
-}
+}
\ No newline at end of file
diff --git a/calendar/inc/class.calendar_zpush.inc.php b/calendar/inc/class.calendar_zpush.inc.php
index 07c858ed6e..82d219590f 100644
--- a/calendar/inc/class.calendar_zpush.inc.php
+++ b/calendar/inc/class.calendar_zpush.inc.php
@@ -84,7 +84,7 @@ class calendar_zpush implements activesync_plugin_write, activesync_plugin_meeti
 	{
 		if (!isset($this->calendar)) $this->calendar = new calendar_boupdate();
 
-		$cals_pref = $GLOBALS['egw_info']['user']['preferences']['activesync']['calendar-cals'];
+		$cals_pref = $GLOBALS['egw_info']['user']['preferences']['activesync']['calendar-cals'] ?? null;
 		$cals = $cals_pref ? explode(',',$cals_pref) : array('P');	// implicit default of 'P'
 		$folderlist = array();
 
@@ -1751,4 +1751,4 @@ if (isset($_SERVER['SCRIPT_FILENAME']) && realpath($_SERVER['SCRIPT_FILENAME'])
 	}
 	echo "</tbody></table>\n";
 	echo "</body></html>\n";
-}
+}
\ No newline at end of file
diff --git a/importexport/inc/class.importexport_export_csv.inc.php b/importexport/inc/class.importexport_export_csv.inc.php
index 620814a53f..578048197e 100644
--- a/importexport/inc/class.importexport_export_csv.inc.php
+++ b/importexport/inc/class.importexport_export_csv.inc.php
@@ -249,7 +249,7 @@ class importexport_export_csv implements importexport_iface_export_record
 					break;
 				case 'date':
 				case 'date-time':
-					if ($c_field['values']['format'])
+					if (!empty($c_field['values']['format']))
 					{
 						// Date has custom format.  Convert so it's standard, don't do normal processing
 						$type = $c_field['type'];
@@ -312,7 +312,7 @@ class importexport_export_csv implements importexport_iface_export_record
 	{
 		if($appname)
 		{
-			if(!self::$cf_parse_cache[$appname])
+			if(empty(self::$cf_parse_cache[$appname]))
 			{
 				$c_fields = self::convert_parse_custom_fields($record, $appname, $selects, $links, $methods);
 				self::$cf_parse_cache[$appname] = array($c_fields, $selects, $links, $methods);
@@ -343,7 +343,7 @@ class importexport_export_csv implements importexport_iface_export_record
 		}
 		foreach($fields['select'] ?? [] as $name)
 		{
-			if($record->$name != null && is_array($selects) && $selects[$name])
+			if($record->$name != null && is_array($selects) && !empty($selects[$name]))
 			{
 				$record->$name = is_string($record->$name) ? explode(',', $record->$name) : $record->$name;
 				if(is_array($record->$name))
@@ -368,7 +368,7 @@ class importexport_export_csv implements importexport_iface_export_record
 		}
 		foreach($fields['links'] ?? [] as $name) {
 			if($record->$name) {
-				if(is_numeric($record->$name) && !$links[$name]) {
+				if(is_numeric($record->$name) && empty($links[$name])) {
 					$link = Link::get_link($record->$name);
 					$links[$name] = ($link['link_app1'] == $appname ? $link['link_app2'] : $link['link_app1']);
 					$record->$name = ($link['link_app1'] == $appname ? $link['link_id2'] : $link['link_id1']);
@@ -428,13 +428,13 @@ class importexport_export_csv implements importexport_iface_export_record
 			{
 				$dec_separator = $GLOBALS['egw_info']['user']['preferences']['common']['number_format'][0];
 				if (empty($dec_separator)) $dec_separator = '.';
-				$thousands_separator = $GLOBALS['egw_info']['user']['preferences']['common']['number_format'][1];
+				$thousands_separator = $GLOBALS['egw_info']['user']['preferences']['common']['number_format'][1] ?? '';
 			}
 			if($record->$name && (string)$record->$name != '')
 			{
 				if(!is_numeric($record->$name))
 				{
-					$record->$name = floatval(str_replace($dec_separator, '.', preg_replace('/[^\d'.preg_quote($dec_separator).']/', '', $record->$name)));
+					$record->$name = (float)(str_replace($dec_separator, '.', preg_replace('/[^\d'.preg_quote($dec_separator, '/').']/', '', $record->$name)));
 				}
 				$record->$name = number_format(str_replace(' ','',$record->$name), 2,
 					$dec_separator,$thousands_separator
@@ -514,4 +514,4 @@ class importexport_export_csv implements importexport_iface_export_record
 
 	}
 } // end  export_csv_record
-?>
+?>
\ No newline at end of file
diff --git a/infolog/inc/class.infolog_so.inc.php b/infolog/inc/class.infolog_so.inc.php
index c1bd5bcd03..b242305170 100644
--- a/infolog/inc/class.infolog_so.inc.php
+++ b/infolog/inc/class.infolog_so.inc.php
@@ -798,7 +798,7 @@ class infolog_so
 		// query children independent of action
 		if (empty($query['col_filter']['info_id_parent']))
 		{
-			$action = isset($action2app[$query['action']]) ? $action2app[$query['action']] : ($query['action'] ?? null);
+			$action = isset($action2app[$query['action']??null]) ? $action2app[$query['action']] : ($query['action'] ?? null);
 			if ($action)
 			{
 				$links = Link\Storage::get_links($action=='sp'?'infolog':$action,
@@ -947,7 +947,7 @@ class infolog_so
 		$pid = 'AND ' . $this->db->expression($this->info_table,array('info_id_parent' => ($action == 'sp' ?$query['action_id'] : 0)));
 
 		if ($GLOBALS['egw_info']['user']['preferences']['infolog']['listNoSubs'] != '1' && $action != 'sp' ||
-			(string)$query['col_filter']['info_id_parent'] !== '' ||
+			($query['col_filter']['info_id_parent']??'') !== '' ||
 			 isset($query['subs']) && $query['subs'] || $action != 'sp' && !empty($query['search']))
 		{
 			$pid = '';
@@ -1096,4 +1096,4 @@ class infolog_so
 		}
 		return $users;
 	}
-}
+}
\ No newline at end of file
diff --git a/notifications/inc/class.notifications.inc.php b/notifications/inc/class.notifications.inc.php
index 6120a14cc7..5d6c6344fd 100644
--- a/notifications/inc/class.notifications.inc.php
+++ b/notifications/inc/class.notifications.inc.php
@@ -502,7 +502,7 @@ class notifications {
 			$backend_errors = array();
 			try {
 				// system or non-system user
-				if($receiver->account_id && is_numeric($receiver->account_id)) {
+				if(!empty($receiver->account_id) && is_numeric($receiver->account_id)) {
 					// system user, collect data and check for Status and expire state, skip notification if expired or not active
 					$userData = $GLOBALS['egw']->accounts->read($receiver->account_id);
 					//error_log(__METHOD__.__LINE__." fetched data for User:".array2string($userData['account_lid']).'#'.$userData['account_type'].'#'.$userData['account_status'].'#'.$GLOBALS['egw']->accounts->is_expired($userData).'#');
@@ -560,7 +560,7 @@ class notifications {
 						if(!file_exists(EGW_INCLUDE_ROOT.'/'. self::_appname.'/inc/class.'. $notification_backend. '.inc.php')) {
 							throw new Exception('file for '.$notification_backend. ' does not exist');
 						}
-						$obj = new $notification_backend( $this->sender, $receiver, $this->config, $preferences );
+						$obj = new $notification_backend( $this->sender, $receiver, $this->config, $preferences??null );
 						if ( !($obj instanceof notifications_iface) ) {
 							unset ( $obj );
 					 		throw new Exception($notification_backend. ' is no implementation of notifications_iface');
@@ -575,7 +575,7 @@ class notifications {
 						} elseif ($backend == 'email') {
 							if (!empty($this->reply_to)) $popup_data = array( 'reply_to' => $this->reply_to );
 						}
-						$obj->send($this->prepend_message($messages, $prepend_message), $lsubject, $llinks, $this->attachments, $popup_data);
+						$obj->send($this->prepend_message($messages, $prepend_message), $lsubject, $llinks, $this->attachments, $popup_data??null);
 
 						// This is to make popup_or_email option sensfull since
 						// we save popup notifications in database anyway, email
@@ -730,7 +730,7 @@ class notifications {
 					break;
 				default:
 					$param = $backend.'_enable';
-					$enabled_backends[$backend] = $this->config->{$param} == true ? true : false;
+					$enabled_backends[$backend] = !empty($this->config->{$param});
 					break;
 			}
 		}
@@ -867,4 +867,4 @@ class notifications {
 
 		return $result;
 	}
-}
+}
\ No newline at end of file
diff --git a/notifications/inc/class.notifications_ajax.inc.php b/notifications/inc/class.notifications_ajax.inc.php
index 577da8ea09..507516abd1 100644
--- a/notifications/inc/class.notifications_ajax.inc.php
+++ b/notifications/inc/class.notifications_ajax.inc.php
@@ -254,7 +254,7 @@ class notifications_ajax {
 	private function get_egwpopup($browserNotify = false)
 	{
 		$entries = notifications_popup::read($this->recipient->account_id);
-		$this->response->apply('app.notifications.append', array($entries['rows'], $browserNotify, $entries['total']));
+		$this->response->apply('app.notifications.append', array($entries['rows']??[], $browserNotify, $entries['total']??0));
 		return true;
 	}
 
@@ -283,4 +283,4 @@ class notifications_ajax {
 		Api\Cache::setSession(self::_appname, 'session_data', $this->session_data);
 		return true;
 	}
-}
+}
\ No newline at end of file
diff --git a/notifications/inc/class.notifications_email.inc.php b/notifications/inc/class.notifications_email.inc.php
index 082eb44ae6..68dde5c87c 100644
--- a/notifications/inc/class.notifications_email.inc.php
+++ b/notifications/inc/class.notifications_email.inc.php
@@ -97,8 +97,8 @@ class notifications_email implements notifications_iface {
 	 */
 	public function send(array $_messages, $_subject = false, $_links = false, $_attachments = false, $_data = false)
 	{
-		$body_plain = $_messages['plain'].$this->render_links($_links, false, $this->preferences->external_mailclient);
-		$body_html = "<html><body>\n".$_messages['html'].$this->render_links($_links, true, $this->preferences->external_mailclient)."</body>\n</html>\n";
+		$body_plain = $_messages['plain'].$this->render_links($_links, false, $this->preferences->external_mailclient??false);
+		$body_html = "<html><body>\n".$_messages['html'].$this->render_links($_links, true, $this->preferences->external_mailclient??false)."</body>\n</html>\n";
 
 		$this->mail->ClearAddresses();
 		$this->mail->ClearAttachments();