If the header is false, this line gives `undefined`

[Matias Malbergier]

jquery-ui-multiselect-widget/src/jquery.multiselect.js

Line 1194 in 58cae16

 var headerHeight = $header.outerHeight(true); 

If header is set to false, the headerHeight has undefined, and then the maxHeight has undefined

[Matias Malbergier]

This line fixes the issue:
if (typeof(headerHeight) !== 'number') { headerHeight = 0; }