Produce an error if the `--type` flag was set, but an empty value
was passed.
Before this patch:
docker inspect --type "" foo
# json output
docker inspect --type unknown foo
"unknown" is not a valid value for --type
With this patch:
docker inspect --type "" foo
type is empty: must be one of "config", "container", "image", "network", "node", "plugin", "secret", "service", "task", "volume"
docker inspect --type unknown foo
unknown type: "unknown": must be one of "config", "container", "image", "network", "node", "plugin", "secret", "service", "task", "volume"
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
