Handle comment to address the incosistent behaviour

Author: ArpitSachan

mongoengine/queryset/base.py

@@ -298,17 +298,20 @@ def first(self):
             result = None
         return result
 
-    def last(self, *ordering_keys):
-        """Retrieve the latest object matching the query.
+    def last(self):
+        """Retrieve the latest object matching the query."""
+        if not self._ordering:
+            raise OperationError("Cannot use `last()` without ordering. Use `order_by()` on the queryset first.")
 
-        :param keys: fields to order the query results by; keys may be
-            prefixed with "+" or a "-" to determine the ordering direction.
-
-        """
-        if not ordering_keys:
-            ordering_keys = "-id"
+        queryset = self.clone()
+        if self._none or self._empty:
+            return None
 
-        return self.order_by(ordering_keys).first()
+        try:
+            result = queryset[-1]
+        except IndexError:
+            result = None
+        return result
 
     def insert(
         self, doc_or_docs, load_bulk=True, write_concern=None, signal_kwargs=None