code: public static Context withValue(Context context, @javax.annotation.Nullable Span span) {
      return Utils.checkNotNull(context, "context").withValue(CONTEXT_SPAN_KEY, span);
    }
docs: Creates a new {@code Context} with the given value set.
  
  @param context the parent {@code Context}.
  @param span the value to be set.
  @return a new context with the given value set.
  @since 0.21