Ios Mantle - doing initWithDictionary correctly by default

I am facing the following problem.

I have class Menu.h and Item.h. The menu is similar to a restaurant menu and has multiple categories (like appetizers, salads, etc.), and each menu has multiple items. So Menu.h has an NSArray property called itemList. I am trying to automatically load these objects using the mantle.

Menu.h

@interface Menu : MTLModel <MTLJSONSerializing>
@property (nonatomic) NSArray *itemList;
@end

      

        
        
        
      

    

AND

Menu.m

@implementation Menu
+ (NSDictionary *)JSONKeyPathsByPropertyKey
{
    // model_property_name : json_field_name
    return @{
             };
}

+ (NSValueTransformer *)itemListJSONTransformer {
    return [NSValueTransformer mtl_JSONArrayTransformerWithModelClass: Item.class];
}

- (instancetype)initWithDictionary:(NSDictionary *)dictionaryValue error:(NSError **)error {
    self = [super initWithDictionary:dictionaryValue error:error];
    if (self == nil) return nil;
    return self;
}

      

        
        
        
      

    

and

Item.m

- (instancetype)initWithDictionary:(NSDictionary *)dictionaryValue error:(NSError **)error {
    self = [super initWithDictionary:dictionaryValue error:error];
    if (self == nil) {
      //DO SOMETHING WITH SELF AND RETURN A NON NIL OBJECT
      return self;
    } 
    return self;
}

      

        
        
        
      

    

My question is the following: if itemList is null, i.e. from a null response from the server comes for itemList and then I want to override the default initWithDictionary behavior to DO ANYTHING AND RETURN A NON-ILLEGAL OBJECT from the Item constructor. h how should i do this? The code doesn't get to that constructor to my surprise because it was null when Menu.h was being formed. I also specified (NSValueTransformer) .. Any leads? Thank!