public Builder mergeFrom(org.box2d.proto.Box2D.PbVec2 other) {
        if (other == org.box2d.proto.Box2D.PbVec2.getDefaultInstance()) return this;
        if (other.hasX()) {
          setX(other.getX());
        }
        if (other.hasY()) {
          setY(other.getY());
        }
        this.mergeUnknownFields(other.getUnknownFields());
        return this;
      }