iOS app crashing on [NSNull hasColorGlyphsInRange:attributes:] - ios

Question

I'm facing this exception, and i'm not being able to figure out the problem.
i tried adding exception breakpoint and symbolic breakpoint but it didn't show any more useful data. it's crashing on the main.h return with nothing in the backtrace
this is the exception:
2016-10-20 17:32:58.615 <AppName>[15655:3398242] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSNull hasColorGlyphsInRange:attributes:]: unrecognized selector sent to instance 0x10b1acfb0'
*** First throw call stack:
(
0 CoreFoundation 0x000000010aeef34b __exceptionPreprocess + 171
1 libobjc.A.dylib 0x000000010f90221e objc_exception_throw + 48
2 CoreFoundation 0x000000010af5ef34 -[NSObject(NSObject) doesNotRecognizeSelector:] + 132
3 CoreFoundation 0x000000010ae74c15 ___forwarding___ + 1013
4 CoreFoundation 0x000000010ae74798 _CF_forwarding_prep_0 + 120
5 UIKit 0x000000010d9c66c1 -[UILabel _determineContentsFormat] + 1475
6 UIKit 0x000000010d9c6f9d -[UILabel _evaluateContentsFormat] + 33
7 UIKit 0x000000010d801923 -[UIView(CALayerDelegate) layerWillDraw:] + 65
8 QuartzCore 0x000000010d2c0b26 _ZN2CA5Layer8display_Ev + 146
9 QuartzCore 0x000000010d2b5596 _ZN2CA5Layer17display_if_neededEPNS_11TransactionE + 294
10 QuartzCore 0x000000010d2b5629 _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 35
11 QuartzCore 0x000000010d24362c _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 280
12 QuartzCore 0x000000010d270713 _ZN2CA11Transaction6commitEv + 475
13 QuartzCore 0x000000010d271083 _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 113
14 CoreFoundation 0x000000010ae93e17 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23
15 CoreFoundation 0x000000010ae93d87 __CFRunLoopDoObservers + 391
16 CoreFoundation 0x000000010ae78b9e __CFRunLoopRun + 1198
17 CoreFoundation 0x000000010ae78494 CFRunLoopRunSpecific + 420
18 GraphicsServices 0x0000000111c6fa6f GSEventRunModal + 161
19 UIKit 0x000000010d73df34 UIApplicationMain + 159
20 AppName 0x0000000109998c73 main + 1187
21 libdyld.dylib 0x00000001103f368d start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException

Answer 1

'-[NSNull hasColorGlyphsInRange:attributes:]: unrecognized selector sent to instance 0x10b1acfb0'
This means you've used a NSNull object. From the call stack, maybe a NSNull used as NSString or NSAttributedString. So you need check it before use it.
if (str != [NSNull null]) {
label.text = str
}

Answer 2

are you use this function hasColorGlyphsInRange if you use
try
if ([self respondsToSelector:#selector(hasColorGlyphsInRange:)]) {
//code
}

Answer 3

You need to be able to read and understand error messages.
You are told that someone or something tried to send a message hasColorGlyphsInRange to an instance of NSNull. Even if it is hard to accept because that shouldn't happen, that's the error message and that's what happened.
So you have put an NSNull instance somewhere where you shouldn't have. hasColorGlyphsInRange doesn't seem documented anywhere, so it's something internal to iOS or macOS. But it very much looks like something about text, and there are UILabel methods on the call stack. And there is a layerWillDraw: on the call stack, so it's something trying to draw a UILabel.
UILabels don't get redrawn immediately, but when the system decides to redraw anything. So the most likely thing is that you have set the text of a UILabel to an NSNull object.
And where does the NSNull object come from? Bets are that you are processing JSON and you assume that you are getting a string and don't check for null objects, and that's why you are setting the text of some UILabel to an NSNull instance.