human
Solve the following python programming problem given the following code:
def assert_warns(warning_class = None, callable = None, * args, **kwargs) : 
    "Assert that the given warning class is thrown as a context manager
    or by passing in a callable and its arguments.

    As a context manager:
    >>> with assert_warns():
    ...     warnings.warn('Hey!')

    Passing in a callable:
    >>> def throw_warning():
    ...     warnings.warn('Hey!')
    >>> assert_warns(UserWarning, throw_warning)
    " 
    if (args is None) : 
        return _assert_warns_context_manager (warning_class = warning_class) 
else : 
        with _assert_warns_context_manager (warning_class = warning_class) : 
            callable (* args, ** kwargs) 

    
    

    Fix the buggy line: if (args is None) :
assistant
#Here is Python code to fix the buggy line: if (args is None) :
.

if (callable is None) :