checkbox is causing error in Jade

I am having trouble with something that should be pretty simple I think. I am making this form and i get a 500 internal server error when i add a checkbox input to the second form group.

This works:

div
    h3 {{questionData.squestion || questionData.equestion}}
form.form-horizontal(ng-submit='submitAnswers(answerArray)')
    div.form-group(ng-repeat='answer in questionData.answers')
        label.col-xs-3 {{answer}}:
        input(type='checkbox' ng-model='answerArray[$index]' ng-change='update(answerArray[$index], answer, this)')
    div.form-group(ng-show = 'questionData.sweighted || questionData.eweighted')
        | hello world
    button.btn.btn-success.strong-button(type='submit') Submit

I get a 500 internal server error when I add the checkbox:

div
    h3 {{questionData.squestion || questionData.equestion}}
form.form-horizontal(ng-submit='submitAnswers(answerArray)')
    div.form-group(ng-repeat='answer in questionData.answers')
        label.col-xs-3 {{answer}}:
        input(type='checkbox' ng-model='answerArray[$index]' ng-change='update(answerArray[$index], answer, this)')
    div.form-group(ng-show = 'questionData.sweighted || questionData.eweighted')
        input(type='checkbox') Hello world
    button.btn.btn-success.strong-button(type='submit') Submit

The internal server error is not giving me any more information either. Just a whole bunch of jquery and angular call stack stuff in my developer console. Am i missing something obvious here? This code is a partial, so this is the full file.