What does the warning message "o.s.web.servlet.PageNotFound : No mapping for HEAD /" mean?

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This warning message means that a client has sent a request using the HTTP HEAD method to the server for a resource that the server is not aware of, and hence does not have a URL mapping for it. The server cannot fulfill the request and responds with a 404 Not Found error. The client should use a valid URL that the server has a mapping for to access the desired resource.