private com.google.protobuf.SingleFieldBuilder<
          org.box2d.proto.Box2D.PbVec2, org.box2d.proto.Box2D.PbVec2.Builder, org.box2d.proto.Box2D.PbVec2OrBuilder> 
          getTargetFieldBuilder() {
        if (targetBuilder_ == null) {
          targetBuilder_ = new com.google.protobuf.SingleFieldBuilder<
              org.box2d.proto.Box2D.PbVec2, org.box2d.proto.Box2D.PbVec2.Builder, org.box2d.proto.Box2D.PbVec2OrBuilder>(
                  target_,
                  getParentForChildren(),
                  isClean());
          target_ = null;
        }
        return targetBuilder_;
      }