Project fork causes a 500 error

Summary

We are testing Gitlab's rest apis and find some internal error. We hope to improve GitLab with open source community workers.

Steps to reproduce

you can create a new project and then fork from itself

curl -X POST -H 'PRIVATE-TOKEN: <YOUR-TOKEN>' 'http://host/api/v4/projects

curl -X POST -H 'PRIVATE-TOKEN: <YOUR-TOKEN>' 'http://host/api/v4/projects/<PROJECT_ID>/fork/<PROJECT_ID>'

What is the current bug behavior?

What is the expected correct behavior?

return 400 Bad Request