Replace all NSNull objects in an NSDictionary

I've made a few changes to Jacob's original answer to extend it to handle dictionaries and arrays stored within the original dictionary.

#import "NSDictionary+NullReplacement.h"#import "NSArray+NullReplacement.h"@implementation NSDictionary (NullReplacement)- (NSDictionary *)dictionaryByReplacingNullsWithBlanks {    const NSMutableDictionary *replaced = [self mutableCopy];    const id nul = [NSNull null];    const NSString *blank = @"";        for (NSString *key in self) {        id object = [self objectForKey:key];        if (object == nul) [replaced setObject:blank forKey:key];        else if ([object isKindOfClass:[NSDictionary class]]) [replaced setObject:[object dictionaryByReplacingNullsWithBlanks] forKey:key];        else if ([object isKindOfClass:[NSArray class]]) [replaced setObject:[object arrayByReplacingNullsWithBlanks] forKey:key];    }    return [NSDictionary dictionaryWithDictionary:[replaced copy]];}@end

And there's also an array category of course:

#import "NSArray+NullReplacement.h"#import "NSDictionary+NullReplacement.h"@implementation NSArray (NullReplacement)- (NSArray *)arrayByReplacingNullsWithBlanks  {    NSMutableArray *replaced = [self mutableCopy];    const id nul = [NSNull null];    const NSString *blank = @"";    for (int idx = 0; idx < [replaced count]; idx++) {        id object = [replaced objectAtIndex:idx];        if (object == nul) [replaced replaceObjectAtIndex:idx withObject:blank];        else if ([object isKindOfClass:[NSDictionary class]]) [replaced replaceObjectAtIndex:idx withObject:[object dictionaryByReplacingNullsWithBlanks]];        else if ([object isKindOfClass:[NSArray class]]) [replaced replaceObjectAtIndex:idx withObject:[object arrayByReplacingNullsWithBlanks]];    }    return [replaced copy];}@end

With this, you can take any array or dictionary and recursively wipe out all the [NSNull null] instances.

P.S. For completion's sake, here are the header files:

@interface NSDictionary (NullReplacement)- (NSDictionary *)dictionaryByReplacingNullsWithBlanks;@end

And the array header:

@interface NSArray (NullReplacement)- (NSArray *)arrayByReplacingNullsWithBlanks;@end

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];

Rolling through the dictionary hunting for NSNull is one way to tackle the problem, but I took a slightly lazier approach. Instead of nil you could assign an empty string, but the principle is the same.

CPJSONDictionary.h

@interface NSDictionary (CPJSONDictionary)- (id)jsonObjectForKey:(id)aKey;@end

CPJSONDictionary.m

@implementation NSDictionary (CPJSONDictionary)- (id)jsonObjectForKey:(id)aKey {    id object = [self objectForKey:aKey];    if ([object isKindOfClass:[NSNull class]]) {        object = nil;    }    return object;}@end