<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _retrieve_value(self, entity, default=None):
 """Internal helper to retrieve the value for this Property from an entity. This returns None if no value is set, or the default argument if given. For a repeated Property this returns a list if a value is set, otherwise None. No additional transformations are applied. """

    return entity._values.get(self._name, default)