Make `value` suitable for a dictionary.

    * If `value` is an Entity, call to_dict() on it.
    * If value is a timestamp, turn it into a string value.
    * If none of the above are satisfied, return the input value

def _dictify(field, value):
    """Make `value` suitable for a dictionary.

    * If `value` is an Entity, call to_dict() on it.
    * If value is a timestamp, turn it into a string value.
    * If none of the above are satisfied, return the input value
    """
    if value is None:
        return None
    elif field.type_:
        return value.to_dict()
    return field.dict_value(value)