Steps to Reproduce

no reproducing scenario at the moment (original code unavailable), but happens during unbind workflow.

Original scenario involve tree, possibly unloaded treeItems with popup / tooltips

Current Result

If undoVParent is called on a widget that doesn't currently have an associated dom element (ROD, etc), the el variable will be undefined:

https://github.com/zkoss/zk/blob/v9.5.1.3/zk/src/archive/web/js/zk/dom.js#L1768

This will cause the typeError:

cannot read property z_vp of undefined.

Expected Result

check if el exists / vparent exists before executing

Debug Information

error happens at:

https://github.com/zkoss/zk/blob/v9.5.1.3/zk/src/archive/web/js/zk/dom.js#L1769

Workaround

	<script><![CDATA[
		zk.afterLoad("zk", function () {
		    var _xzjq = {};
		    zk.override(zjq.prototype, _xzjq, {
		        undoVParent: function() {
		        	var el = this.jq[0];
	        		if(!this.hasVParent() || !el){
	        			console.log("skip undoVparent")
	        			return;
	        		}
					var result = _xzjq.undoVParent.apply(this, arguments);
					return result;
		        }
		     });
		});
	]]></script>