RestKit无法使用＆＃39; NULL＆＃39;结果

Question

我有RestKit这个问题，我无法弄明白。我正在尝试使用null结果映射对象，但RestKit由于某种原因无法处理该对象。我知道我做错了什么，但我无法弄清楚是什么。

这是我从服务中获得的回复：

{"responseError":null}

这是ResponseError.h文件：

@interface ResponseError : NSObject
@property (nonatomic,assign) NSInteger applicationErrorCode;
@property (nonatomic,strong) NSString *developerMessage;
@property (nonatomic,strong) NSString *userMessage;
@end

这是ResponseWithError.h文件：

@interface ResponseWithError : NSObject
@property (nonatomic,strong) ResponseError *responseError;
@end

这是对象的映射：

RKObjectMapping *responseErrorMapping = [RKObjectMapping mappingForClass:[ResponseError class]];
[responseErrorMapping addAttributeMappingsFromDictionary:@{ @"applicationErrorCode" : @"applicationErrorCode", @"developerMessage" : @"developerMessage",@"userMessage" : @"userMessage"}];

RKRelationshipMapping *responseErrorRelationMapping = [RKRelationshipMapping relationshipMappingFromKeyPath:@"responseError" toKeyPath:@"responseError" withMapping:responseErrorMapping];


RKObjectMapping *checkR = [RKObjectMapping mappingForClass:[ResponseWithError class]];
    [checkR addPropertyMapping:[responseErrorRelationMapping copy]];
    [[RKObjectManager sharedManager] addResponseDescriptor:[RKResponseDescriptor responseDescriptorWithMapping:checkR
method:RKRequestMethodPOST pathPattern:[RequestStringBuilder approveStatementChecks]  keyPath: nil
statusCodes: RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)]];

这是我从RestKit获得的错误：

"No mappable object representations were found at the key paths searched."

提前致谢。