For an environment variable defined in the yaml without value, the value needs to be propagated from the client, as in Docker Compose. Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
Signed-off-by: Santhosh Manohar <santhosh@docker.com>
Signed-off-by: allencloud <allen.sun@daocloud.io>