validate doesn't flag files that don't exist

[jsoref]

{
...
  "Sources": {
    "foo": "local/path/to/file1",
...
  },
...
}

$ daisy  -validate no-foo.wf.json
[Daisy] Validating workflow "package-no-foo"
[package-no-foo]: 2018/03/20 18:19:23 Validating workflow
[package-no-foo]: 2018/03/20 18:19:23 Validating step "setup-disk"
[package-no-foo]: 2018/03/20 18:19:23 Validating step "create-disk-from-image"
[package-no-foo]: 2018/03/20 18:19:23 Validating step "translate-disk-inst"
[package-no-foo]: 2018/03/20 18:19:24 Validation Complete

$ daisy  no-foo.wf.json
[Daisy] Running workflow "package-no-foo"
[package-no-foo]: 2018/03/20 18:19:58 Validating workflow
[package-no-foo]: 2018/03/20 18:19:58 Validating step "create-disk-from-image"
[package-no-foo]: 2018/03/20 18:19:58 Validating step "setup-disk"
[package-no-foo]: 2018/03/20 18:19:59 Validating step "translate-disk-inst"
[package-no-foo]: 2018/03/20 18:19:59 Validation Complete
[package-no-foo]: 2018/03/20 18:19:59 Using the GCS path gs://...-daisy-bkt/daisy-package-no-foo-20180320-22:19:58-47ss8
[package-no-foo]: 2018/03/20 18:19:59 Uploading sources
[package-no-foo]: 2018/03/20 18:19:59 Error uploading sources: FileIOError: stat .../local/path/to/file1: no such file or directory
[package-no-foo]: 2018/03/20 18:19:59 Workflow "package-no-foo" cleaning up (this may take up to 2 minutes).

[Daisy] Errors in one or more workflows:
  package-no-foo: FileIOError: stat .../local/path/to/file1: no such file or directory

[Zyqsempai]

So, should we just return error message similar to [Daisy] Errors in one or more workflows: package-no-foo: FileIOError: stat .../local/path/to/file1: no such file or directory ?