Javascript error on event registration

When selecting an event fee on the registration form, a javascript error occurs:

fillTotalAmount is not defined

This is triggered by onclick="fillTotalAmount(FEEAMOUNT)" in the fee input fields (where FEEAMOUNT is a number). Presumably this is supposed to calculate a total for price sets, but when a price set is not used, there is no total field and the function is not present.

It doesn't seem to prevent the registration completing and the error is usually ignored on Firefox and Chrome, etc. On Internet Explorer, however, js errors are reported as standard, therefore this could be confusing for users.