List grid allowed to unselect all the listgrid columns.

Hi,

We are using Smart Gwt-4.1p (29th Oct 2014)
Browser: Google chrome 39.0.2171.95 m, IE8 and IE9

I have one listgrid which is having 3 columns(Col-A, Col-B and Col-C). All three columns are displayed(Visible) in the list grid.

We have an option to un-select each column(Click on column header right corner >> Columns).But it is allowed me to un select all the columns(Col-A, Col-B and Col-C) and after unselected all the columns i have no option to revert back the changes.

How to avoid un-selecting all the columns,
In the above case if two columns(Col-A, Col-B) are un selected third column(Col-C) should not allow to un select and should be greyed out.

Please let us know if any possibility is there to achieve the above behaviour.
Thanks in Advance....

Note: For you reference please find the attached screen shot.

Regards,

Attached Images

AllowedToUnseletallthecolumns.jpg (17.5 KB)