Error when closing when not saving unsaved message

[sander]

When I close Coccinella with a message dialog opened, it asks me if I want to save that message. When I click "No" I get the following error and Coccinella is not closed:

can't use empty string as operand of "!"
can't use empty string as operand of "!"
    while executing
"if {![::UserActions::DoQuit -warning 1]} {
     set result stop
 }"
    (procedure "::JUI::CloseHook" line 6)
    invoked from within
"::JUI::CloseHook .jmain"
    ("uplevel" body line 1)
    invoked from within
"uplevel #0 $topcache($w,-closecommand) $w"
    (procedure "::UI::DoCloseWindow" line 24)
    invoked from within
"::UI::DoCloseWindow .jmain wm"
    (command for "WM_DELETE_WINDOW" window manager protocol)

[Mats (matsben)]

I didn't reproduce it but found a flaw in ::UserActions::DoQuit which returned empty (and not 0|1) in one of its branches.