<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_variation_for_experiment(self, experiment_id):
 """ Helper method to retrieve variation ID for given experiment. Args: experiment_id: ID for experiment for which variation needs to be looked up for. Returns: Variation ID corresponding to the experiment. None if no decision available. """


    return self.experiment_bucket_map.get(experiment_id, {self.VARIATION_ID_KEY: None}).get(self.VARIATION_ID_KEY)