I got problems with the same chunk of code. My problem was that I was
using a form which didn't have a specific value, here's Twitter, for
example:

    <input type="hidden" name="scribe_log">

When trying to do a URL encode of that field, we'd try to construct a
pair but end up with:

    '(scribe_log)

Which would fail at encoding. It should encode to the same as
scribe_log having an empty value, that is "scribe_log=" and so should
be parsed as '(scribe_log "") - I've attached a patch which fixes
that.