public SerializableFunction<Row, T> getFromRowFunction() {
    return fromRowFunction;
  }
@Test
  public void testNullMapRowToProto() {
    ProtoDynamicMessageSchema schemaProvider = schemaFromDescriptor(MapPrimitive.getDescriptor());
    SerializableFunction<Row, DynamicMessage> fromRow = schemaProvider.getFromRowFunction();
    MapPrimitive proto =
        parseFrom(fromRow.apply(NULL_MAP_PRIMITIVE_ROW).toString(), MapPrimitive.newBuilder())
            .build();
    assertEquals(NULL_MAP_PRIMITIVE_PROTO, proto);
  }