From my point of view a "XY not found" is not an error. At the current state of the API it is hard to differentiate between "XY not found" and an error *(except by parsing error messages -> what I don't dare to do)*. **Example requirement** :point\_right: Return a project if it exists or create it otherwise. As far as I know this very simple requirement is not possible with the current API implementation! Given the project doesn't exist: Trying to retrieve the project to check if it exists and to potentially return it would yield a unrelatable error response that I'm unable to handle properly. Given the project does exist: Just trying to create the project every time would also yield a error but wouldn't return the actual existing project. **Proposal** If I access XY with the necessary and validated permissions and non other error appears but the requested XY doesn't exists: * return a empty response * OR return a specific error code that can be handled *(if 404 and 204 are used for anything else then introduce a new 9xx custom error code)* ~"feature proposal" gitlab-ce~2677507