Running artifact-cache image fails

Trying to run an artifact cache using the docker image, by following these steps https://gitlab.com/BuildStream/buildstream-docker-images/#setting-up-a-buildstream-artifact-cache-with-docker

I get the following

Generating a 4096 bit RSA private key
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writing new private key to '/home/artifacts/keys/server.key'
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E1212 15:58:43.170657321       8 ssl_transport_security.cc:628] Could not load any root certificate.
E1212 15:58:43.170695775       8 ssl_transport_security.cc:1849] Invalid verification certs.
E1212 15:58:43.170715271       8 ssl_security_connector.cc:461] Handshaker factory creation failed with TSI_INVALID_ARGUMENT.
E1212 15:58:43.170737229       8 server_secure_chttp2.cc:84] {"created":"@1544630323.170724064","description":"Unable to create secure server with credentials of type Ssl.","file":"src/core/ext/transport/chttp2/server/secure/server_secure_chttp2.cc","file_line":63,"security_status":1}

(btw, there is a typo in the instructions, missing \ at the end of line)