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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_current_async():
 """Return a reference to the currently executing Async job object or None if not in an Async job. """

    local_context = _local.get_local_context()

    if local_context._executing_async:
        return local_context._executing_async[-1]

    raise errors.NotInContextError('Not in an _ExecutionContext.')