I was talking to a Chinese friend yesterday and said 没事 to him. He gave me a puzzled look. When I told him I was trying to say "It doesn't matter" he said, "Ah! You mean 没事儿." I mean he added 儿化 to the end of 没事. Does this mean that it is wrong not to add 儿化 to 没事, just like in 一会儿 and 一块儿? Obviously I am talking about standard Mandarin (普通话).