Parse "key cannot be nil" error on [PFObject saveInBackground] (Cocoa) - cocoa

Question

I'm trying out the Parse SDK in an existing Mac OS X application. I followed the setup steps in the Parse Quickstart guide, including adding an import for the Parse library to my AppDelegate .m file and calling:
[Parse setApplicationId:kParseApplicationID clientKey:kParseClientKey];
in the applicationDidFinishLaunching method. The two constants I use are defined in a Constants file which is also imported.
Towards the end the guide says: "Then copy and paste this code into your app, for example in the viewDidLoad method (or inside another method that gets called when you run your app)"
So I imported the Parse header file into my main view controller .m file and copied and pasted their code into its viewDidLoad method:
PFObject *testObject = [PFObject objectWithClassName:#"TestObject"];
testObject[#"foo"] = #"bar";
[testObject saveInBackground];
When this runs, I hit an exception whose message is "setObjectForKey: key cannot be nil" on that last line. Not on the previous line where I'm actually setting the object for the key. Furthermore, if I stop on the previous line and PO testObject, testObject.allKeys, or testObject[#"foo"], they all show non-nil values for the key "foo". And still furthermore, if I move this code to the end of the AppDelegate's applicationDidFinishLaunching method, the code executes without any errors, and the TestObject shows up in my Parse application dashboard.
Can somebody tell me what I'm doing wrong? I'd really like to explore further, but this is a real blocker for me.
Here's the console log from a slightly more involved OS X app, also occurring on [ParseObject saveInBackgroundWithBlock:]:
2015-06-03 16:55:56.046 TestApp [15795:15954566] An uncaught exception was raised
2015-06-03 16:55:56.046 TestApp [15795:15954566] *** setObjectForKey: key cannot be nil
2015-06-03 16:55:56.046 TestApp [15795:15954566] (
0 CoreFoundation 0x00007fff8fb0103c __exceptionPreprocess + 172
1 libobjc.A.dylib 0x00007fff978e476e objc_exception_throw + 43
2 CoreFoundation 0x00007fff8f9e7c66 -[__NSDictionaryM setObject:forKey:] + 1174
3 ParseOSX 0x000000010011adbb __74-[PFMultiProcessFileLockController beginLockedContentAccessForFileAtPath:]_block_invoke + 129
4 libdispatch.dylib 0x000000010026cd43 _dispatch_client_callout + 8
5 libdispatch.dylib 0x000000010026e0b1 _dispatch_barrier_sync_f_invoke + 348
6 ParseOSX 0x000000010011ad15 -[PFMultiProcessFileLockController beginLockedContentAccessForFileAtPath:] + 127
7 ParseOSX 0x00000001000f61ea +[PFObject(Private) _objectFromDataFile:error:] + 207
8 ParseOSX 0x000000010010f231 +[PFUser(Private) _getCurrentUserWithOptions:] + 611
9 ParseOSX 0x00000001000fc4bd -[PFObject(Private) saveAsync:] + 118
10 ParseOSX 0x00000001000e1d25 -[PFTaskQueue enqueue:] + 188
11 ParseOSX 0x00000001000ff06b -[PFObject saveInBackground] + 121
12 ParseOSX 0x00000001000ff270 -[PFObject saveInBackgroundWithBlock:] + 49
13 TestApp 0x0000000100001827 +[SBTParseTranslation saveDBObjectToParse:] + 183
14 TestApp 0x0000000100031fb4 -[SWBMainWindowViewController showRecordForItem:] + 3124
15 TestApp 0x0000000100031268 -[SWBMainWindowViewController showRecordForID:] + 184
16 TestApp 0x0000000100031080 -[SWBMainWindowViewController finishLoad] + 448
17 TestApp 0x0000000100030eb1 -[SWBMainWindowViewController loadData] + 97
18 TestApp 0x0000000100030dd5 -[SWBMainWindowViewController viewDidLoad] + 725

Answer 1

This was caused by a case of confusion on my part. I work mostly on iOS projects, where applicationDidFinishLaunching can typically be counted on to have run before viewControllers load. Apparently that isn't the case in OS X apps.
In short, I was calling the ParseObject save methods before [Parse setApplicationID: clientKey] had been called.

Answer 2

In my case ios7 was crashing with saveInBackground since podfile contained:
platform :ios, '8.0'
and deployment target was 7.0. I replaced with
platform :ios, '7.0'
then clean and build again