Fix #3213 Rest arg is not optional (#3303)

tests/shell/pipeline/commands/internal.rs

@@ -278,6 +278,19 @@ fn run_custom_command_with_rest_and_flag() {
     assert_eq!(actual.out, r#"["world","hello","yay"]"#);
 }
 
+#[test]
+fn run_custom_command_with_empty_rest() {
+    let actual = nu!(
+        cwd: ".",
+        r#"
+            def rest-me-with-empty-rest [...rest: string] { echo $rest }; rest-me-with-empty-rest
+        "#
+    );
+
+    assert_eq!(actual.out, r#""#);
+    assert_eq!(actual.err, r#""#);
+}
+
 #[test]
 fn set_variable() {
     let actual = nu!(