public final void tag(I input, ScopedSpan span) {
    if (input == null) throw new NullPointerException("input == null");
    if (span == null) throw new NullPointerException("span == null");
    if (span.isNoop()) return;
    tag(span, input, span.context());
  }
@Test void tag_customizer_withNullContext() {
    when(parseValue.apply(eq(input), isNull())).thenReturn("value");

    tag.tag(input, null, customizer);

    verify(parseValue).apply(input, null);
    verifyNoMoreInteractions(parseValue); // doesn't parse twice
    verify(customizer).tag("key", "value");
    verifyNoMoreInteractions(customizer); // doesn't tag twice
  }