hflex cause slider without width to throw "Not allowed to set hflex and width" exception

when setting a hflex on a slider, even with width="null", the exception:
Not allowed to set hflex and width at the same time except hflex="min"
will be thrown.

maybe due to a default width of 200 in slider class constructor.

reproduced with zul:

<zk>
<slider hflex="1"/>
</zk>