11539 empty lookup handle non boolean params

[arthanson]

Fixes: #11539

The issue requested that a 404 be returned, but IMHO this is not consistent with how other filter params work, if you filter on "region_id=ss" it won't 404 but just return no values from the query. This change uses strtobool "True values are y, yes, t, true, on and 1; false values are n, no, f, false, off and 0" for anything else it interprets it as false. Also cleaned up the return string to make it a bit easier to read what exactly is going on. Unfortunately strtobool raises a ValueError if the string doesn't match a valid input, so needed to wrap that.

[jeremystretch]

Rather than invoking strtobool(), it may be preferable to remain as consistent with Django as possible by replicating the logic of its own BooleanField class. This would effectively treat anything other than the strings "false" or "0" (after calling lower()) as true.

[jeremystretch]

After digging into this a bit, it's unfortunately going to require a lot more work to resolve. The lookup itself should only accept boolean values; the validation should happen in the filter. I've opened PR #11784 to capture my work toward a resolution, however more work remains to be done.