js error on contribution form with no payment

to recreate:

• create a contribution form
• disable real time monetary transactions and all contrib fields on the Amounts tab
• enable a membership
• view the form

there is a js console error because a block of javascript is loaded that works with payment fields (a change() function on the payment_processor_id) – but because payments are disabled the form element isn't loaded and it errors.

test form here: http://dmaster.demo.civicrm.org/civicrm/contribute/transact?reset=1&id=4