code: @Override public <C> void inject(SpanContext spanContext, Format<C> format, C carrier) {
      Injector<TextMap> injector = formatToInjector.get(format);
      if (injector == null) {
        throw new UnsupportedOperationException(format + " not in " + formatToInjector.keySet());
      }
      TraceContext traceContext = ((BraveSpanContext) spanContext).unwrap();
      injector.inject(traceContext, (TextMap) carrier);
    }
docs: Injects the underlying context using B3 encoding by default.