setNilValueForKey：could not set nil as the value for the key distance.解决方案

重写这个方法
- (void)setNilValueForKey:(NSString *)key;

-(void)setNilValueForKey:(NSString *)key{

    if ([key isEqualToString:@"originalPrice"]) {
        _originalPrice = 0;
    }else {
        [super setNilValueForKey:key];
}
}