corrected changed_when handling

lib/ansible/executor/task_executor.py

@@ -447,12 +447,10 @@ class TaskExecutor:
 
             # helper methods for use below in evaluating changed/failed_when
             def _evaluate_changed_when_result(result):
-                if self._task.changed_when:
+                if self._task.changed_when is not None and self._task.changed_when:
                     cond = Conditional(loader=self._loader)
                     cond.when = self._task.changed_when
                     result['changed'] = cond.evaluate_conditional(templar, vars_copy)
-                else:
-                    result['changed'] = False
 
             def _evaluate_failed_when_result(result):
                 if self._task.failed_when: