SimpleHtmlEditorField breaks JavaScript

[jrast]

If I add a SimpleHtmlEditorField to my Form (with SimpleHtmlEditorField::create('TestField')) the javascript breaks as it tries to load a file from the location http://localhost/undefined.

[jrast]

Ok, I have found the part which leads to this problem:
In bootstrap_forms.js Line 14 we want to set the content_css, but in the second part

$t.attr('data-css')

is undefined as I don't set it on the field with

->setCSS('file');

So what is the best solution to only set this if it's not undefined?