I want to implement a case in which incident should not get saved unitl and unless a kb is attached

[PriyanshuS64936]

//This should be only when assignment group is service desk.

//Here's the code I have written but when using this , it is throwing the error even after attaching the kb

function onSubmit() {

var kb=g_form.getValue('knowledge_base');

var assignmentGroup = g_form.getDisplayValue('assignment_group');

if (assignmentGroup && assignmentGroup.toLowerCase() ==='service desk'){

if (!kb){

g_form.addErrorMessage('You must attach a <b>Knowledge Base</b> before saving this incident');

return false;

}

}

return true;

}