function mxVssxCodec(editorUi) {
                    var _this = _super.call(this) || this;
                    _this.RESPONSE_END = "";
                    _this.RESPONSE_DIAGRAM_START = "";
                    _this.RESPONSE_DIAGRAM_END = "";
                    _this.RESPONSE_HEADER = "";
                    _this.editorUi = editorUi;
                    return _this;
                }
Post processes groups to remove leaf vertices that render nothing
@param group
@param {mxGraph} graph