删除非空资源时出现正确的HTTP错误

我认为正确的答案是409冲突。

The request could not be completed due to a conflict with the current state of 
the resource. This code is only allowed in situations where it is expected 
that the user might be able to resolve the conflict and resubmit the request. 
The response body SHOULD include enough information for the user to recognize 
the source of the conflict. Ideally, the response entity would include enough 
information for the user or user agent to fix the problem; however, that might 
not be possible and is not required.

http://www.restapitutorial.com/httpstatuscodes.html 表示只要满足请求会导致资源冲突,就应该使用409。重复条目和在不支持级联删除时删除根对象是两个示例。