Steps to Reproduce

1. load the zul below
2. click the button twice

<zk>

<tree width="400px" height="120px">
	<treecols>
		<treecol width="200px" label="1" />
		<treecol id="secondCol" label="2" />
	</treecols>
	<treechildren>
		<treeitem forEach="A, B, C, D, E">
			<treerow>
				<treecell label="${each}" />
				<treecell label="${each}" />
			</treerow>
		</treeitem>
	</treechildren>
</tree>
	<button label="Zoom" onClick='secondCol.setWidth(secondCol.getWidth() == null ? "500px" : null)' />
</zk>

Current Result

Uncaught TypeError: Cannot read property 'indexOf' of null
at init._isAllWidths (zul.mesh.wpd:1103)
at init._adjSpanWd (zul.mesh.wpd:1221)
at init._calcSize (zul.mesh.wpd:1010)
at init.onSize (zul.mesh.wpd:885)
at init.$supers (zk.wpd:10776)
at init.onSize (zul.sel.wpd:3005)
at _invoke (zk.wpd:12829)
at init.fire (zk.wpd:12812)
at _fire (zk.wpd:12955)
at Object.fireDown (zk.wpd:13052)
_isAllWidths @ zul.mesh.wpd:1103
_adjSpanWd @ zul.mesh.wpd:1221
_calcSize @ zul.mesh.wpd:1010
onSize @ zul.mesh.wpd:885
$supers @ zk.wpd:10776
onSize @ zul.sel.wpd:3005
_invoke @ zk.wpd:12829
fire @ zk.wpd:12812
_fire @ zk.wpd:12955
fireDown @ zk.wpd:13052
fireDown @ zk.wpd:14354
fireSized @ zk.wpd:14924
replaceHTML @ zk.wpd:16720
$supers @ zk.wpd:10776
replaceHTML @ zul.mesh.wpd:746
rerender @ zk.wpd:16783
_rerender0 @ zk.wpd:15477
setTimeout (async)
_rerender @ zk.wpd:15461
rerender @ zk.wpd:16752
updateMesh_ @ zul.mesh.wpd:2083
_zkf @ zul.mesh.wpd:2059
(anonymous) @ zk.wpd:9889
_set2 @ zk.wpd:10333
setter.func @ zk.wpd:15882
zk.Widget.zk.$extends.set @ zk.wpd:15910
setAttr @ zk.wpd:21156
doProcess @ zk.wpd:20103
doCmdsNow @ zk.wpd:20347
_doCmds @ zk.wpd:20603
afterResponse @ zk.wpd:20238
onResponseReady @ zk.wpd:20235
XMLHttpRequest.send (async)
ajaxSendNow @ zk.wpd:20299
sendNow @ zk.wpd:20761
(anonymous) @ zk.wpd:20277
setTimeout (async)
ajaxSend2 @ zk.wpd:20277
ajaxSend @ zk.wpd:20271
send @ zk.wpd:20521
sendAU_ @ zk.wpd:17480
fireX @ zk.wpd:17459
doClick_ @ zk.wpd:26003
_doEvt @ zk.wpd:19556
(anonymous) @ zk.wpd:19750
dispatch @ zk.wpd:5157
elemData.handle @ zk.wpd:4828

Expected Result

no js error

Debug Info

since our javadoc allows to set width with null, there should be no javascript error

public void setWidth(java.lang.String width)
Sets the width. If null, the best fit is used.

Root Cause

w._width === undefined

Workaround

the attached js