In addition to @Malk, I wanted to clear all fields in the popup, except the hidden fields. To do that just use this:
$('.modal').on('hidden.bs.modal', function () {
$(this)
.find("input:not([type=hidden]),textarea,select")
.val('')
.end()
.find("input[type=checkbox], input[type=radio]")
.prop("checked", "")
.end();
});
This will clear all fields, except the hidden ones.