public Builder mergeGroundAnchorB(org.box2d.proto.Box2D.PbVec2 value) {
        if (groundAnchorBBuilder_ == null) {
          if (((bitField0_ & 0x00100000) == 0x00100000) &&
              groundAnchorB_ != org.box2d.proto.Box2D.PbVec2.getDefaultInstance()) {
            groundAnchorB_ =
              org.box2d.proto.Box2D.PbVec2.newBuilder(groundAnchorB_).mergeFrom(value).buildPartial();
          } else {
            groundAnchorB_ = value;
          }
          onChanged();
        } else {
          groundAnchorBBuilder_.mergeFrom(value);
        }
        bitField0_ |= 0x00100000;
        return this;
      }