human
Solve the following python programming problem given the following code:
def _create_collection_loader(self, context, key, _instance) : 
    def load_collection_from_joined_new_row(state, dict_, row) : 
        collection = attributes.init_state_collection (state, dict_, key) 
        result_list = util.UniqueAppender (collection, 'append_without_event') 
        context.attributes [(state, key)] = result_list 
        _instance (row, result_list) 
def load_collection_from_joined_existing_row(state, dict_, row) : 
        if ((state, key) in context.attributes) : 
            result_list = context.attributes [(state, key)] 
else : 
            collection = attributes.init_state_collection (state, dict_, key) 
            result_list = util.UniqueAppender (collection, 'append_without_event') 
            context.attributes [(state, key)] = result_list 
_instance (row, result_list) 
def load_collection_from_joined_exec(state, dict_, row) : 
        _instance (row, None) 
return (load_collection_from_joined_new_row, load_collection_from_joined_existing_row, None, <MASK>) 
    
    Given the code above, what is a proper replacement for <MASK>? Choose among: _instance, self, load_collection_from_joined_new_row, context, load_collection_from_joined_existing_row, key
assistant
#Here is a proper replacement for <MASK>.
def load_collection_from_joined_exec(