human
Solve the following python programming problem given the following code:
def _TestParallelInstanceCreationAndRemoval(max_instances = None, disk_template = None, custom_job_driver = None) : 
    'Tests parallel creation and immediate removal of instances.

  @type max_instances: int
  @param max_instances: maximum number of instances to create
  @type disk_template: string
  @param disk_template: disk template for the new instances or C{None} which
                        causes the default disk template to be used
  @type custom_job_driver: _JobQueueDriver
  @param custom_job_driver: a custom L{_JobQueueDriver} to use if not L{None}.
                            If one is specified, C{WaitForCompletion} is _not_
                            called on it.

  ' 
    job_driver = (instance_generator or _JobQueueDriver ()) 
    def _CreateSuccessFn(instance, job_driver, _) : 
        job_id = _SubmitInstanceRemoveJob (instance) 
        job_driver.AddJob (job_id) 
instance_generator = _AcquireAllInstances () 
    if (max_instances is not None) : 
        instance_generator = itertools.islice (instance_generator, max_instances) 
for instance in instance_generator : 
        job_id = _SubmitInstanceCreationJob (instance, disk_template = disk_template) 
        job_driver.AddJob (job_id, success_fn = functools.partial (_CreateSuccessFn, instance)) 
if (custom_job_driver is None) : 
        job_driver.WaitForCompletion () 

    
    

    Fix the buggy line: job_driver = (instance_generator or _JobQueueDriver ())
assistant
#Here is Python program to fix the buggy line: job_driver = (instance_generator or _JobQueueDriver ())
.

job_driver = (custom_job_driver or _JobQueueDriver ())