Fix crash in UserDefaults when setting a nil value.

[Minddol]

NUGU SDK for iOS Environment

• sdk version: 0.28.2

Relevant System Logs

2021-02-18 13:48:22.118409+0900 SampleApp[7954:2715207] [User Defaults] Attempt to set a non-property-list object <null> as an NSUserDefaults/CFPreferences value for key refreshToken
2021-02-18 13:48:22.122642+0900 SampleApp[7954:2715207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Attempt to insert non-property list object null for key refreshToken'
*** First throw call stack:
(
	0   CoreFoundation                      0x00000001052f729b __exceptionPreprocess + 331
	1   libobjc.A.dylib                     0x0000000104419735 objc_exception_throw + 48
	2   CoreFoundation                      0x00000001052f70f5 +[NSException raise:format:] + 197
	3   CoreFoundation                      0x000000010520d1c8 _CFPrefsValidateValueForKey + 312
	4   CoreFoundation                      0x000000010520d65c -[CFPrefsSource setValues:forKeys:count:copyValues:removeValuesForKeys:count:from:] + 380
	5   CoreFoundation                      0x000000010520d9ec -[CFPrefsSource setValues:forKeys:count:copyValues:from:] + 28
	6   CoreFoundation                      0x000000010520da43 -[CFPrefsSource setValue:forKey:from:] + 67
	7   CoreFoundation                      0x00000001052edb7e __108-[_CFXPreferences(SearchListAdditions) withSearchListForIdentifier:container:cloudConfigurationURL:perform:]_block_invoke + 318
	8   CoreFoundation                      0x00000001052ed2ca normalizeQuintuplet + 314
	9   CoreFoundation                      0x00000001052eda34 -[_CFXPreferences(SearchListAdditions) withSearchListForIdentifier:container:cloudConfigurationURL:perform:] + 100
	10  CoreFoundation                      0x00000001052c9c2b -[_CFXPreferences setValue:forKey:appIdentifier:container:configurationURL:] + 91
	11  CoreFoundation                      0x00000001052ce085 _CFPreferencesSetAppValueWithContainer + 117
	12  Foundation                          0x0000000103ebdee1 -[NSUserDefaults(NSUserDefaults) setObject:forKey:] + 55
	13  SampleApp                           0x000000010282a786 $s9SampleApp11UserDefaultV12wrappedValuexvs + 454
	14  SampleApp                           0x000000010286a51f $sSo14NSUserDefaultsC9SampleAppE8StandardO12refreshTokenSSSgvsZ + 127
	15  SampleApp                           0x000000010285caa3 $s9SampleApp18NuguCentralManagerC17authorizationInfo33_FC9167D502BB17DCCE77A4A48EB1C47FLL0C8LoginKit013AuthorizationG0VSgvW + 387
	16  SampleApp                           0x000000010285cb88 $s9SampleApp18NuguCentralManagerC17authorizationInfo33_FC9167D502BB17DCCE77A4A48EB1C47FLL0C8LoginKit013AuthorizationG0VSgvs + 200
	17  SampleApp                           0x000000010285f0ce $s9SampleApp18NuguCentralManagerC5login4from10completionySo16UIViewControllerC_ys6ResultOyytAA0aB5ErrorOGctFyAJy0C8LoginKit17AuthorizationInfoVAN0cmnL0OGcfU0_ + 702
	18  NuguLoginKit                        0x0000000103d10992 $s12NuguLoginKit0A11OAuthClientC9authorize5grant10completionyAA0E16CredentialsGrantV_ys6ResultOyAA17AuthorizationInfoVAA0abC5ErrorOGcSgtFyAJy10Foundation4DataVAN8APIErrorOGcfU_ + 658
	19  NuguLoginKit                        0x0000000103d27b73 $s12NuguLoginKit13ApiProvidablePAAE7request10completionSo20NSURLSessionDataTaskCys6ResultOy10Foundation0I0VAA0abC5ErrorO8APIErrorOGcSg_tFyALSg_So13NSURLResponseCSgs0M0_pSgtcfU2_ + 1667
	20  NuguLoginKit                        0x0000000103d28e48 $s10Foundation4DataVSgSo13NSURLResponseCSgs5Error_pSgIegggg_So6NSDataCSgAGSo7NSErrorCSgIeyByyy_TR + 296
	21  CFNetwork                           0x0000000107dc0ef0 __75-[__NSURLSessionLocal taskForClass:request:uploadFile:bodyData:completion:]_block_invoke + 19
	22  CFNetwork                           0x0000000107dd70bc __49-[__NSCFLocalSessionTask _task_onqueue_didFinish]_block_invoke + 172
	23  Foundation                          0x0000000103e8819d __NSBLOCKOPERATION_IS_CALLING_OUT_TO_A_BLOCK__ + 7
	24  Foundation                          0x0000000103e880a4 -[NSBlockOperation main] + 68
	25  Foundation                          0x0000000103e84e13 -[__NSOperationInternal _start:] + 689
	26  Foundation                          0x0000000103e8ae4a __NSOQSchedule_f + 227
	27  libdispatch.dylib                   0x0000000108d865d1 _dispatch_call_block_and_release + 12
	28  libdispatch.dylib                   0x0000000108d8763e _dispatch_client_callout + 8
	29  libdispatch.dylib                   0x0000000108d8a589 _dispatch_continuation_pop + 565
	30  libdispatch.dylib                   0x0000000108d89963 _dispatch_async_redirect_invoke + 859
	31  libdispatch.dylib                   0x0000000108d98028 _dispatch_root_queue_drain + 351
	32  libdispatch.dylib                   0x0000000108d989cd _dispatch_worker_thread2 + 130
	33  libsystem_pthread.dylib             0x000000010917f9f7 _pthread_wqthread + 220
	34  libsystem_pthread.dylib             0x000000010917eb77 start_wqthread + 15
)
libc++abi.dylib: terminating with uncaught exception of type NSException
Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Attempt to insert non-property list object null for key refreshToken'
terminating with uncaught exception of type NSException

[Minddol]

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