Allowing the wrong type definition does not cause the entire parent node JSONModel to be nil. "// 1) check if property is itself a JSONModel" has the same conditions.

NSString* jsonData = @{@"person":{ @"name": @"joke", @"age": @18, @"desc": [NSNull null]}}; // from server response data

@interface MYJSONModel : JSONModel
@EnD
@implementation MYJSONModel

• (BOOL)propertyIsOptional:(NSString *)propertyName {
  return YES;
  }
  @EnD

@interface PersonItem : MYJSONModel
@Property (nonatomic, copy) NSString* name;
@Property (nonatomic, assign) NSInteger age;
@Property (nonatomic, copy) NSString* desc;
@EnD

@interface PersonInfo : MYJSONModel
@Property (nonatomic, strong) PersonItem* person;
@EnD

NSError* error;
PersonInfo* p = [[PersonInfo alloc] ] initWithDictionary: jsonData error:&error];

NSString* jsonData = @{@"person":{ @"name": @"joke", @"age": @18, @"desc": [NSNull null] }};
server change desc from string to dictionary:
NSString* jsonData = @{@"person":{ @"name": @"joke", @"age": @18, @"desc": @{@"more":@"more detail"} }};

Result: p.person is nil and error is nil.
i want p.person is not nil & p.person.desc could be nil in this case.

when [property.isOptional || !validation] return error should be more careful in traverse properties.