public static MetadataUpdate fromJson(String json) {
    return JsonUtil.parse(json, MetadataUpdateParser::fromJson);
  }
@Test
  public void testAssignUUIDToJson() {
    String action = MetadataUpdateParser.ASSIGN_UUID;
    String uuid = "9510c070-5e6d-4b40-bf40-a8915bb76e5d";
    String json = "{\"action\":\"assign-uuid\",\"uuid\":\"9510c070-5e6d-4b40-bf40-a8915bb76e5d\"}";
    MetadataUpdate expected = new MetadataUpdate.AssignUUID(uuid);
    assertEquals(action, expected, MetadataUpdateParser.fromJson(json));
  }