public SpanCustomizer currentSpanCustomizer() {
    // note: we don't need to decorate the context for propagation as it is only used for toString
    TraceContext context = currentTraceContext.get();
    if (context == null || isNoop(context)) return NoopSpanCustomizer.INSTANCE;
    return new SpanCustomizerShield(toSpan(context));
  }
@Test void currentSpanCustomizer_defaultsToNoop() {
    assertThat(tracer.currentSpanCustomizer())
      .isSameAs(NoopSpanCustomizer.INSTANCE);
  }