Heroku logs on 'Saving problems'.

gistfile1.txt

2013-07-05T11:16:09.177945+00:00 app[web.2]: Started PUT "/problems/51d6882c78c3f738fc000046" for 203.123.164.34 at 2013-07-05 11:16:09 +0000
2013-07-05T11:16:10.446408+00:00 app[web.2]: 
2013-07-05T11:16:10.446408+00:00 app[web.2]: Mongoid::Errors::InvalidFind (
2013-07-05T11:16:10.446408+00:00 app[web.2]: Problem:
2013-07-05T11:16:10.446408+00:00 app[web.2]:   Calling Document.find with nil is invalid.
2013-07-05T11:16:10.446408+00:00 app[web.2]: Summary:
2013-07-05T11:16:10.446408+00:00 app[web.2]:   Document.find expects the parameters to be 1 or more ids, and will return a single document if 1 id is provided, otherwise an array of documents if multiple ids are provided.
2013-07-05T11:16:10.446408+00:00 app[web.2]: Resolution:
2013-07-05T11:16:10.446408+00:00 app[web.2]:   Most likely this is caused by passing parameters directly through to the find, and the parameter either is not present or the key from which it is accessed is incorrect.):
2013-07-05T11:16:10.446408+00:00 app[web.2]:   app/controllers/problems_controller.rb:159:in `block in merge_json_attributes'
2013-07-05T11:16:10.446408+00:00 app[web.2]:   app/controllers/problems_controller.rb:158:in `map'
2013-07-05T11:16:10.446722+00:00 app[web.2]:   app/controllers/problems_controller.rb:158:in `merge_json_attributes'
2013-07-05T11:16:10.446722+00:00 app[web.2]: 
2013-07-05T11:16:10.446722+00:00 app[web.2]: 
2013-07-05T11:16:10.451753+00:00 heroku[router]: at=info method=POST path=/problems/51d6882c78c3f738fc000046 host=ed-socrates.herokuapp.com fwd="203.123.164.34" dyno=web.2 connect=1ms service=4509ms status=500 bytes=643