public static Builder builder() {
    return new Builder();
  }
@Test(expectedExceptions = NullPointerException.class)
  public void testBuilderNoNullProducerThrowExceptions() {
    PinotSourceDataGenerator generator = Mockito.mock(PinotSourceDataGenerator.class);
    PinotRealtimeSource realtimeSource =
        PinotRealtimeSource.builder().setTopic("mytopic").setGenerator(generator).build();
  }