iOS crashing when receiving empty array from Parse.com's CloudCode

I'm attempting to fetch a query from "Parse.com's cloudcode" which returns a dictionary. The dictionary contains two keys, "groups" and "invites", both being arrays.

When one of they key's is an empty array, the following error occurs:

2014-05-23 17:14:03.967 XXX[2267:60b] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '* -[__NSPlaceholderDictionary initWithObjects:forKeys:count:]: attempt to insert nil object from objects[1]' * First throw call stack: (0x2d589f0b 0x37d20ce7 0x2d4c7cff 0x2d4c7ac3 0x1acd5b 0x1acfef 0xddb95 0xdda07 0xedd4d 0x2fdd3d23 0x2fe83057 0x2fdd3d23 0x2fe38e7f 0x2fe38e09 0x2fdb1b73 0x2d555039 0x2d5529c7 0x2d552d13 0x2d4bd769 0x2d4bd54b 0x3242a6d3 0x2fe1c891 0xe3805 0x3821eab7) libc++abi.dylib: terminating with uncaught exception of type NSException (lldb)

Here's the cloud code function:

Parse.Cloud.define("GroupsAndInvites",function(request,response){
        var user = request.user;
        //query memberships and invites for the current user
        var membershipQuery = new Parse.Query("Membership").include("group").equalTo("user",user);
        var inviteQuery = new Parse.Query("Invite").include("from").include("group").equalTo("to",user);

        //make promises
        var membershipPromise = membershipQuery.find();
        var invitePromise = inviteQuery.find();

        //call when both queries are done
        Parse.Promise.when(membershipPromise,invitePromise).then(function(memberships,invites){
                //make an array of groups instead of memberships
                var groups = [];
                for(var i=0;i<memberships.length;i++){
                        groups.push(memberships[i].get("group"));
                }
                //return groups and invites
                response.success({
                        "groups":groups,
                        "invites":invites
                });
        });
});

And here's my implementation of that function on the front end:

  [PFCloud callFunctionInBackground:@"GroupsAndInvites" withParameters:nil block:^(NSDictionary *dict, NSError *error) {
    if (!error) {
      NSMutableArray *groupsArray = [NSMutableArray array];
      NSMutableArray *invitesArray = [NSMutableArray array];

      for (BVYGroup *group in dict[@"groups"]) {
        [groupsArray addObject:group];
      }

      for (BVYInvite *invite in dict[@"invites"]) {
        [invitesArray addObject:invite];
      }

      if ([strongDelegate respondsToSelector:@selector(groupStream:didFetchGroups:andInvites:)]) {
        [strongDelegate groupStream:self didFetchGroups:groupsArray andInvites:invitesArray];
      }
    } else {
      if ([strongDelegate respondsToSelector:@selector(groupStream:didFailToFetchGroupsWithError:)]) {
        [strongDelegate groupStream:self didFailToFetchGroupsWithError:error];
      }
    }
  }];

The error occurs right when a response is retrieved. It does not reach the if statement that checks for an error.

Any insight to why this might be occurring?
Thank you in advance.