throw an error instead of a panic if no input is provided to inspect (#9259)

# Description

This is a small PR to fix Nu crashing when calling `inspect` with no
data piped in(#9255).


# User-Facing Changes

none.

crates/nu-command/src/debug/inspect.rs

@@ -34,6 +34,11 @@ impl Command for Inspect {
     ) -> Result<PipelineData, ShellError> {
         let input_metadata = input.metadata();
         let input_val = input.into_value(call.head);
+        if input_val.is_nothing() {
+            return Err(ShellError::PipelineEmpty {
+                dst_span: call.head,
+            });
+        }
         let original_input = input_val.clone();
         let description = match input_val {
             Value::CustomValue { ref val, .. } => val.value_string(),

crates/nu-command/tests/commands/inspect.rs

@@ -0,0 +1,7 @@
+use nu_test_support::nu;
+
+#[test]
+fn inspect_with_empty_pipeline() {
+    let actual = nu!("inspect");
+    assert!(actual.err.contains("no input value was piped in"));
+}

crates/nu-command/tests/commands/mod.rs

@@ -37,6 +37,7 @@ mod headers;
 mod help;
 mod histogram;
 mod insert;
+mod inspect;
 mod into_filesize;
 mod into_int;
 mod join;