iOS：无法在NSMutableDictionary中设置空值(iOS: can't set the null value in an NSMutableDictionary)

 我试图在NSMutableDictionary设置一个值，但我总是得到这个错误： 
 
Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<__NSDictionaryI 0x10fd55990> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key image.'
 
 在NSMutableDictionary中，我有一个@"image"字段，可以为null 。 我想用占位符图像名称替换null值。 这是我如何做到的： 
 
NSMutableDictionary * item = self.carouselSource[index];
if([Utils isNull:[item valueForKey:@"image"]]) {
[item setValue:@"default_image.png" forKey:@"image"]; 
}
 
 但是应用程序在这一行中崩溃 
 
[item setValue:@"default_image.png" forKey:@"image"];
 
 由于上面的错误。 

I'm trying to set a value in an NSMutableDictionary but I'm always getting this error:
 
Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<__NSDictionaryI 0x10fd55990> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key image.'
 
In the NSMutableDictionary I have an @"image" field that can be null. I want to replace the null value with a placeholder image name. This is how I do it:
 
NSMutableDictionary * item = self.carouselSource[index];
if([Utils isNull:[item valueForKey:@"image"]]) {
[item setValue:@"default_image.png" forKey:@"image"]; 
}
 
But the application crash in this line
 
[item setValue:@"default_image.png" forKey:@"image"];
 
due to the error above. 

原文：https://stackoverflow.com/questions/45633521