rem: this._childIdToElementMap[this.component.children[i].renderId].style.zIndex = index; 
add: var childElement = this._childIdToElementMap[this.component.children[i].renderId]; if (childElement) { childElement.style.zIndex = index; } 
context: EchoRender.ComponentSync.ContentPane.prototype._processZIndexChanged = function(e) {    for (var i = 0; i < this.component.children.length; ++i) {        if (!this.component.children[i].floatingPane) {            continue;        }        var index = this._floatingPaneManager.getIndex(this.component.children[i].renderId);        this._childIdToElementMap[this.component.children[i].renderId].style.zIndex = index;    }};
meta: 600	/local1/tlutelli/issta_data/temp/all_js/javascript/2007_temp/2007/600/b5bacb0abc9d19af1d5a080140cce7553db98592/Render.ContentPane.js/buggy/src/webcontainer/java/nextapp/echo/webcontainer/resource/js/Render.ContentPane.js