'Converts a v3 Filter to a v4 PropertyFilter.
Args:
v3_filter: a datastore_pb.Filter
v4_property_filter: a datastore_v4_pb.PropertyFilter to populate
Raises:
InvalidConversionError if the filter cannot be converted'

def _v3_filter_to_v4_property_filter(self, v3_filter, v4_property_filter):

    check_conversion((v3_filter.property_size() == 1), 'invalid    filter')
    check_conversion((v3_filter.op() <= 5), ('unsupported    filter    op:    %d' % v3_filter.op()))
    v4_property_filter.Clear()
    v4_property_filter.set_operator(v3_filter.op())
    v4_property_filter.mutable_property().set_name(v3_filter.property(0).name())
    self._entity_converter.v3_property_to_v4_value(v3_filter.property(0), True, v4_property_filter.mutable_value())
