Convert to a ``dict``

        Subclasses can override this function.

        Returns:
            Python dict with keys set from this Entity.

def to_dict(self):
        """Convert to a ``dict``

        Subclasses can override this function.

        Returns:
            Python dict with keys set from this Entity.
        """
        entity_dict = {}

        for field, val in six.iteritems(self._fields):
            if field.multiple:
                if val:
                    val = [_dictify(field, x) for x in val]
                else:
                    val = []
            else:
                val = _dictify(field, val)

            # Only add non-None objects or non-empty lists
            if val is not None and val != []:
                entity_dict[field.key_name] = val

        self._finalize_dict(entity_dict)

        return entity_dict