NSDictionary 赋值崩溃

[__NSPlaceholderDictionary initWithObjects:forKeys:count:]: attempt to insert nil object from objects[1]'

NSDictionary创建有两种方法，NSDictionary *dic =@{@"xxx":@"xxx"}；或者NSDictionary *dic =[NSDictionary dictionaryWithObjectsAndKeys:@"xxx",@"xxx",nil];但是用第一种创建的dic里面的元素一定不能为空，否则就会崩溃。。。