get this exception when user try to set a filter on a empty cell, but should it handle by UI, instead of throw an exception?
嚴重的: >>java.lang.RuntimeException: Cannot find the range. Please select a cell within the range and try again!
>> at org.zkoss.zss.model.impl.RangeImpl.autoFilter(RangeImpl.java:2037)
>> at org.zkoss.zss.api.NRange.enableAutoFilter(NRange.java:500)
>> at org.zkoss.zss.essential.ToolbarCtrl.onToggleFilter(ToolbarCtrl.java:1022)
>> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
>> at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
>> at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)

Reproducing Steps:

1. Open Spreadsheet
2. select an empty cell then enable auto-filter

Actual:
the above exception occurs.

Expected: