docs: static StringMap injectContextData(@Nullable List<Property> properties, StringMap reusable) {
      if (properties == null || properties.isEmpty()) {
        return getContextAndTracingData();
      }
      // Context data has precedence over configuration properties.
      putProperties(properties, reusable);
      // TODO(sebright): The following line can be optimized. See
      //     https://github.com/census-instrumentation/opencensus-java/pull/1422/files#r216425494.
      reusable.putAll(getContextAndTracingData());
      return reusable;
    }