Replace all NSNull objects in an NSDictionary

I'm curious, I currently have an NSDictionary where some values are set to an NSNull object thanks to the help of json-framework.

The aim is to strip all NSNull values and replace it with an empty string.

I'm sure someone has done this somewhere? No doubt it is probably a four liner and is simple, I am just far too burnt out to figure this out on my own.

Really simple:

@interface NSDictionary (JRAdditions)
- (NSDictionary *)dictionaryByReplacingNullsWithStrings;
@end

@implementation NSDictionary (JRAdditions)

- (NSDictionary *)dictionaryByReplacingNullsWithStrings {
   const NSMutableDictionary *replaced = [self mutableCopy];
   const id nul = [NSNull null];
   const NSString *blank = @"";

   for(NSString *key in self) {
      const id object = [self objectForKey:key];
      if(object == nul) {
         //pointer comparison is way faster than -isKindOfClass:
         //since [NSNull null] is a singleton, they'll all point to the same
         //location in memory.
         [replaced setObject:blank 
                      forKey:key];
      }
   }

   return [replaced copy];
}

@end

Usage:

NSDictionary *someDictThatHasNulls = ...;
NSDictionary *replacedDict = [someDictThatHasNulls dictionaryByReplacingNullsWithStrings];