@Nullable public static BaggageField getByName(@Nullable TraceContext context, String name) {
    if (context == null) return null;
    return ExtraBaggageContext.getFieldByName(context, validateName(name));
  }
@Test void getByName_invalid() {
    assertThatThrownBy(() -> BaggageField.getByName(context, ""))
      .isInstanceOf(IllegalArgumentException.class);
    assertThatThrownBy(() -> BaggageField.getByName(context, "    "))
      .isInstanceOf(IllegalArgumentException.class);
  }