cli: prevent empty environment variable keys
cli: prevent empty environment variable keys

Signed-off-by: Nick Sandford <75ef9faee755c70589550b513ad881e5a603182c@sandford.id.au>

flynn/flynn,flynn/flynn,flynn/flynn,philiplb/flynn,lmars/flynn,flynn/flynn,lmars/flynn,philiplb/flynn,lmars/flynn,lmars/flynn,philiplb/flynn,flynn/flynn,philiplb/flynn,philiplb/flynn,lmars/flynn