[bug 933786] Fix strip error

[willkg]

We get this weird error on input-stage (and only on stage) where someone
is using the Input API and sending in nonsensical POST data and it
somehow manages to result in attrs['device'] being None which causes an
error.

I spent some time looking into it and I can't figure out how it ends up
as a None. I don't know what the actual input that's causing the error
is.

Regardless, this alleviates that by making sure it's a unicode but it's
goofipants.

r?

[willkg]

I'm totally game for other ideas here.

[rlr]

This branch fixes the issue for me

$ curl -X POST -H "Content-Type: application/json" -d '{"happy":true,"description":"awesome", "product": "Firefox OS", "device":null}' http://localhost:8000/api/v1/feedback/
{"happy": true, "url": "", "description": "awesome", "product": "Firefox OS", "channel": "", "version": "", "locale": "", "platform": "", "country": "", "manufacturer": "", "device": "", "email": ""}

r+

[willkg]

^^^ That redoes the fix with a much better fix that prevents nulls for all the fields.

r?

[rlr]

$ curl -X POST -H "Content-Type: application/json" -d '{"happy":true,"description":"awesome", "product": "Firefox OS", "device":null}' http://localhost:8000/api/v1/feedback/
{"device": ["Value cannot be null"]}

r+!

[willkg]

2324aa3 [bug 933786] Fix strip error