human
Solve the following python programming problem given the following code:
def block_until_build_queue_empty(self, timeout = 60) : 
    "
        This blocks until the master's build queue is empty. This data is exposed via the /queue endpoint and contains
        any jobs that are currently building or not yet started. If the queue is not empty before the timeout, this
        method raises an exception.

        :param timeout: The maximum number of seconds to block before raising an exception.
        :type timeout: int
        " 
    master_api = UrlBuilder (queue_url._master_url) 
    queue_url = master_api.url ('queue') 
    def is_queue_empty() : 
        queue_resp = requests.get (queue_url) 
        if (queue_resp and queue_resp.ok) : 
            queue_data = queue_resp.json () 
            if (('queue' in queue_data) and (len (queue_data ['queue']) == 0)) : 
                return True 
return False 
if (not poll.wait_for (is_queue_empty, timeout, 0.5)) : 
        raise Exception ('Master service did not become idle before timeout.') 

    
    

    Fix the buggy line: master_api = UrlBuilder (queue_url._master_url)
assistant
#Here is Python code to fix the buggy line: master_api = UrlBuilder (queue_url.

master_api = UrlBuilder (self._master_url)