Fixed clippy warning

src/types/maybe_undefined.rs

@@ -143,7 +143,7 @@ impl<T> MaybeUndefined<T> {
         match self {
             MaybeUndefined::Value(y) => matches!(x, Some(v) if v == y),
             MaybeUndefined::Null => matches!(x, None),
-            _ => false,
+            MaybeUndefined::Undefined => false,
         }
     }