@Override public boolean equals(Object o) {
      if (o == this) return true;
      if (o instanceof Constant) {
        Constant that = (Constant) o;
        return Objects.equals(this.v, that.v);
      }
      return false;
    }
Returns a copy of this object, so you can make an identical follow-up request.
zipkin/src/main/java/zipkin2/Call.java