human
Solve the following python programming problem given the following code:
def dir_extractor(node) : 
    def buildDirEmptyCase(source_ref) : 
        if node.getParentVariableProvider ().isCompiledPythonModule () : 
            source = ExpressionBuiltinGlobals (source_ref = source_ref) 
else : 
            source = ExpressionBuiltinLocals (source_ref = source_ref) 
result = ExpressionCallEmpty (called = ExpressionAttributeLookup (source = source, attribute_name = 'keys', source_ref = source_ref), source_ref = source_ref) 
        if (python_version >= 300) : 
            result = ExpressionBuiltinList (value = result, source_ref = source_ref) 
return result 
return BuiltinOptimization.extractBuiltinArgs (node = node, builtin_class = ExpressionBuiltinDir1, builtin_spec = BuiltinOptimization.builtin_dir_spec, empty_special_class = <MASK>) 
    
    Given the code above, what is a proper replacement for <MASK>? Choose among: node
assistant
#Here is a proper replacement for <MASK>.
def buildDirEmptyCase(