public Builder addJoints(org.box2d.proto.Box2D.PbJoint value) {
        if (jointsBuilder_ == null) {
          if (value == null) {
            throw new NullPointerException();
          }
          ensureJointsIsMutable();
          joints_.add(value);
          onChanged();
        } else {
          jointsBuilder_.addMessage(value);
        }
        return this;
      }