avoids printing blank diffs

fixes #10147 fixes #9471

lib/ansible/plugins/callback/default.py

@@ -109,7 +109,7 @@ class CallbackModule(CallbackBase):
         self._display.banner(msg)
 
     def v2_on_file_diff(self, result):
-        if 'diff' in result._result:
+        if 'diff' in result._result and result._result['diff'] != {}:
             self._display.display(self._get_diff(result._result['diff']))
 
     def v2_playbook_item_on_ok(self, result):

lib/ansible/plugins/callback/minimal.py

@@ -77,5 +77,5 @@ class CallbackModule(CallbackBase):
         self._display.display("%s | UNREACHABLE!" % result._host.get_name(), color='yellow')
 
     def v2_on_file_diff(self, result):
-        if 'diff' in result._result:
+        if 'diff' in result._result and result._result['diff'] != {}:
             self._display.display(self._get_diff(result._result['diff']))