Why does this app crash if I'm testing for the cause and bypassing the offending code?

Question

I have this code where I'm trying to get all records for a certain key:

//  if the apptObject.aApptKey is nil, skip it...
if(apptObject.aApptKey == nil)
    continue;  //  go to beginning and try again 

    //  using apptObject.aApptKey, get the client's name
NSPredicate *predicate =  ([NSPredicate predicateWithFormat:@"(aClientKey = %@)", apptObject.aApptKey]);
    clientInfo = [ClientInfo MR_findAllWithPredicate: predicate];

The problem is I'm getting this error (courtesy of Crashlytics):

Fatal Exception: NSInvalidArgumentException +entityForName: nil is not a legal NSManagedObjectContext parameter searching for entity name 'ClientInfo'

Either don't understand what the error message is telling me, or I don't understand how it could happen if I'm testing for nil prior to the MR_findAll. Note that the 'keys' in question are exactly the same, I'm just using the appointment key to get the client's name.

Can someone please explain how this could happen?

Answer 1

(From my comment:) The error message has nothing to do with the predicate. It tells you that the NSManagedObjectContext is nil.

A possible problem could be the MR_contextForCurrentThread method which is deprecated and should not be used anymore. The reason is that it assumes a unique thread for each managed object context. This is no longer true with the new MOC concurrency types which run on GCD queues. Compare https://stackoverflow.com/a/20536335/1187415.

Better use MR_defaultContext or pass the context from one view controller to the next.