filter_checkbox sends filter value =null on first deselect

[helgasoft]

Being on the receiving end of filter_checkbox, it was a surprise to get a null instead of [ ] or [all keys] on first checkbox de-select. Workaround on our end:

ct_filter =  new crosstalk.FilterHandle();
ct_filter.on('change', function(e) {    // external keys to filter
   if (e.value == undefined) e.value = [];  ...

Subsequent de-selects are sending [all keys] as expected.

Could issue be related to this code line ...?