(from "busybox")
(env ["--unset"] "FOO" "BAR")
(env ["--unset=true"] "FOO")
(env ["--unset=false"] "FOO" "bar" "=")
(label ["--unset"] "foo" "bar.baz")
(label ["--unset=false"] "foo" "bar" "=")
(volume ["--unset"] "/foo" "/bar")
(volume ["--unset"] "/foo" "/bar")
(onbuild (env ["--unset"] "FOO"))
