NSInternalInconsistencyException: -[__NSCFDictionary setObject:forKey:]: mutating method sent to immutable object

[jwalgran]

https://rollbar.com/Azavea/OpenTreeMap/items/3472/

NSInternalInconsistencyException: -[__NSCFDictionary setObject:forKey:]: mutating method sent to immutable object
1 CoreFoundation in 0x22af2000
2 libobjc.A.dylib in 0x22380000
3 CoreFoundation in 0x22af2000
4 CoreFoundation in 0x22af2000
5 OpenTreeMap "OTMSplashViewController.m" line 31 in -[OTMSplashViewController loadInstance]
6 OpenTreeMap "OTMLoginManager.m" line 33 in -[OTMLoginManager init]
7 UIKit in 0x27153000
8 PhotoLibrary in 0x2c5ea000
9 PhotoLibrary in 0x2c5ea000
10 PhotoLibrary in 0x2c5ea000
11 PhotoLibrary in 0x2c5ea000
12 UIKit in 0x27153000
13 UIKit in 0x27153000
14 UIKit in 0x27153000
15 UIKit in 0x27153000
16 UIKit in 0x27153000
17 UIKit in 0x27153000
18 UIKit in 0x27153000
19 UIKit in 0x27153000
20 CoreFoundation in 0x22af2000
21 CoreFoundation in 0x22af2000
22 CoreFoundation in 0x22af2000
23 CoreFoundation in 0x22af2000
24 CoreFoundation in 0x22af2000
25 GraphicsServices in 0x240e2000
26 UIKit in 0x27153000
27 OpenTreeMap "AZTileCacheKey.m" line 22 in -[AZTileCacheKey(Private) cacheKey]