Swagger : TypeError: Failed to fetch

I am trying to define a simple API which is pretty much an healthcheck. My problem is that the requests is correct, the answer I receive from the server is correct, but it is not displayed by swagger : http://imgur.com/a/pgTL4

Here's what the answer I get (which is correct) : http://imgur.com/a/qPLZy and the HTTP status is 200 : http://imgur.com/a/LmIpf

Also,I have defined the HTTP status 200 and 500 : http://imgur.com/a/eaxfr

Would anyone have a hint ? Thanks.