Raise a clear error for an empty command line (#1618) #3061

Job	Run time
Linters (pydocstyle)	21s
No leftovers	3m 48s
build_test_container	11m 29s
cwltool release test	16m 28s
Linters (lintreadme)	32s
Test on macos-latest	2m 34s
CWL conformance (v1.2, podman)	10m 3s
Tox (3, 11, unit)	6m 32s
CWL conformance (v1.0, docker)	8m 7s
CWL conformance (v1.1, singularity)	41m 38s
Linters (shellcheck)	13s
CWL conformance (v1.1, podman)	8m 35s
CWL conformance (v1.2, docker)	41m 38s
Tox (3, 10, mypy)	9m 42s
Tox (3, 13, lint)	50s
Tox (3, 13, bandit)	32s
Tox (3, 11, mypy)	4m 17s
Tox (3, 11, lint)	41m 38s
Tox (3, 14, lint)	41m 39s
CWL conformance (v1.0, singularity)	2m 59s
Tox (3, 12, bandit)	42s
CWL conformance (v1.1, docker)	7m 25s
Tox (3, 14, mypy)	9m 29s
CWL conformance (v1.3.0-dev1, --relax-path-checks)	11m 20s
Tox (3, 14, bandit)	41m 39s
Tox (3, 10, bandit)	41m 38s
Tox (3, 13, mypy)	9m 43s
Tox (3, 10, unit)	4m 22s
Tox (3, 14, unit)	41m 39s
Tox (3, 13, unit)	41m 39s
Tox (3, 12, unit)	41m 38s
CWL conformance (v1.0, podman)	7m 49s
Tox (3, 12, mypy)	41m 39s
Tox (3, 10, lint)	40s
Tox (3, 12, lint)	34s
CWL conformance (v1.2, docker, --fast-parser)	41m 38s
Tox (3, 11, bandit)	41m 38s
CWL conformance (v1.2, singularity)	41m 38s
	11h 20m 25s

Provide feedback