public Builder toBuilder() {
    Builder result = new Builder();
    result.flags = flags;
    result.traceIdHigh = traceIdHigh;
    result.traceId = traceId;
    return result;
  }
@Test void canSetSampledNull() {
    base = base.toBuilder().sampled(true).build();

    TraceIdContext objects = base.toBuilder().sampled(null).build();

    assertThat(objects.debug())
      .isFalse();
    assertThat(objects.sampled())
      .isNull();
  }