How to remove a null value from NSDictionary

Iterate through the dictionary and look for any null entries and remove them.

NSMutableDictionary *prunedDictionary = [NSMutableDictionary dictionary];
for (NSString * key in [yourDictionary allKeys])
{
    if (![[yourDictionary objectForKey:key] isKindOfClass:[NSNull class]])
        [prunedDictionary setObject:[yourDictionary objectForKey:key] forKey:key];
}

After that, prunedDictionary should have all non-null items in the original dictionary.

Here is my category-based recursive solution for dictionaries containing dictionaries and arrays which values can also be dictionaries and arrays:

File NSDictionary+Dario.m:

#import "NSArray+Dario.h"

@implementation NSDictionary (Dario)

- (NSDictionary *) dictionaryByReplacingNullsWithEmptyStrings {

    const NSMutableDictionary *replaced = [NSMutableDictionary new];
    const id nul = [NSNull null];
    const NSString *blank = @"";

    for(NSString *key in self) {
        const id object = [self objectForKey:key];
        if(object == nul) {
            [replaced setObject:blank forKey:key];
        } else if ([object isKindOfClass:[NSDictionary class]]) {
            [replaced setObject:[object dictionaryByReplacingNullsWithEmptyStrings] forKey:key];
        } else if ([object isKindOfClass:[NSArray class]]) {
            [replaced setObject:[object arrayByReplacingNullsWithEmptyStrings] forKey:key];
        } else {
            [replaced setObject:object forKey:key];
        }
    }
    return [NSDictionary dictionaryWithDictionary:(NSDictionary*)replaced];
}

@end

File NSArray+Dario.m:

#import "NSDictionary+Dario.h"

@implementation NSArray (Dario)

- (NSArray *) arrayByReplacingNullsWithEmptyStrings {
    const NSMutableArray *replaced = [NSMutableArray new];
    const id nul = [NSNull null];
    const NSString *blank = @"";

    for (int i=0; i<[self count]; i++) {
        const id object = [self objectAtIndex:i];

        if ([object isKindOfClass:[NSDictionary class]]) {
            [replaced setObject:[object dictionaryByReplacingNullsWithEmptyStrings] atIndexedSubscript:i];
        } else if ([object isKindOfClass:[NSArray class]]) {
            [replaced setObject:[object arrayByReplacingNullsWithEmptyStrings] atIndexedSubscript:i];
        } else if (object == nul){
            [replaced setObject:blank atIndexedSubscript:i];
        } else {
            [replaced setObject:object atIndexedSubscript:i];
        }
    }
    return [NSArray arrayWithArray:(NSArray*)replaced];
}

Use this for remove null from dictionary

- (NSMutableDictionary *)recursive:(NSMutableDictionary *)dictionary {
for (NSString *key in [dictionary allKeys]) {    
    id nullString = [dictionary objectForKey:key];   
    if ([nullString isKindOfClass:[NSDictionary class]]) {
        [self recursive:(NSMutableDictionary*)nullString];
    } else {
        if ((NSString*)nullString == (id)[NSNull null])
            [dictionary setValue:@"" forKey:key];
    }
}
return dictionary;
}

Another variation, without (explicit) loop:

NSMutableDictionary *dict = [yourDictionary mutableCopy];
NSArray *keysForNullValues = [dict allKeysForObject:[NSNull null]];
[dict removeObjectsForKeys:keysForNullValues];