human
Solve the following python programming problem given the following code:
@ classmethod 
@ gen.coroutine 
def _NotifyUsersWithContact(cls, client, name, identity_key, timestamp) : 
    'Adds a notification to all users having contacts with the specified identity. Invalidates
    all contacts added after the specified timestamp.
    ' 
    @ gen.coroutine 
    def _VisitContactUserId(contact_user_id) : 
        (yield NotificationManager.CreateForUser (client, contact_user_id, name, invalidate = invalidate)) 
invalidate = { 
        'contacts' : { 
            'start_key' : Contact.CreateSortKey (None, timestamp), 
}, 
} 
    (yield gen.Task (Contact.VisitContactUserIds, invalidate, identity_key, _VisitContactUserId)) 

    
    

    Fix the buggy line: (yield gen.Task (Contact.VisitContactUserIds, invalidate, identity_key, _VisitContactUserId))
assistant
#Here is Python program to fix the buggy line: (yield gen.

(yield gen.Task (Contact.VisitContactUserIds, client, identity_key, _VisitContactUserId))