We have code that reacts to window resize and repaints part of our DOM. The tooltip code also reacts and tries to reposition itself, assuming old anchor target is still there.

Code:
<body style="padding:0;margin:0">
<h3 id="foo" class="foo">Dependency editor demo</h3>
<script>
    
        t = new Ext.tip.ToolTip({
            delegate   : '.foo', 
 target : document.body,
            showDelay  : 0,
            anchor     : 'bottom',
            trackMouse : false,
            html : 'foasfsa'
        });

        t.render(document.body)
        Ext.fly(window).on('resize', function () {
            Ext.get('foo').destroy();
        }, null, { single : true });

        t.anchorTo(Ext.get('foo'));
</script>
</body>
Error:
Code:
ext-all-debug.js:30746 Uncaught TypeError: Cannot read property 'el' of null
    at constructor.getAlignToRegion (ext-all-debug.js:30746)
    at constructor.alignTo (ext-all-debug.js:31507)
    at constructor.action (ext-all-debug.js:31462)
    at constructor.fire (ext-all-debug.js:21551)
    at constructor.doFireEvent (ext-all-debug.js:22524)
    at constructor.prototype.doFireEvent (ext-all-debug.js:63103)
    at constructor.fireEventArgs (ext-all-debug.js:22377)
    at constructor.fireEvent (ext-all-debug.js:22336)
    at constructor.fireResize (ext-all-debug.js:54197)
    at call (ext-all-debug.js:21063)
Ext.tip.Tooltip needs to check if anchorToEl exists/is garbage before showing on window resize.
Code:
anchorTo: function(anchorToEl, alignment, offsets, animate, monitorScroll, callback) {
        var me = this,
            scroll = !Ext.isEmpty(monitorScroll),
            action = function() {
                me.mixins.positionable.alignTo.call(me, anchorToEl, alignment, offsets, animate);
                Ext.callback(callback, me);
            },
            anchor = me.getAnchor();