@Nullable public String getValue(@Nullable TraceContext context) {
    if (context == null) return null;
    return this.context.getValue(this, context);
  }
@Test void getValue_extracted_invalid() {
    assertThatThrownBy(() -> REQUEST_ID.getValue((TraceContextOrSamplingFlags) null))
      .isInstanceOf(NullPointerException.class);
  }