second object of each pair must be non-nil. Or

아래와 같은 오류가 떴다. 2019-09-04 15:08:46.196386+0900 JeungObjc[5524:730049] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSPlaceholderArray initWithObjects:count:]: attempt to insert nil object from objects[0]' *** First throw call stack: ( 0 CoreFoundation 0x00000001051878db __exceptionPreprocess + 331 1 libobjc.A.dylib 0x000000010472aac5 objc_exception..