ERROR: Bad --suppress value: JSC_DUPLICATE_NAMESPACE

I'm trying to compile a generated javascript protobuf file, and getting this error that I'm trying to suppress:

```
bazel-out/k8-fastbuild/bin/external/com_github_stackb_grpc_js/js/pb/pb.i.js:2076: ERROR - Duplicate namespace: jspb.Message
goog.provide("jspb.Message");
^
Codes: JSC_DUPLICATE_NAMESPACE
```

However, including this suppress code causes a different error `ERROR: Bad --suppress value: JSC_DUPLICATE_NAMESPACE`:

```
suppress = [
"JSC_DUPLICATE_NAMESPACE",
],
```

Trying to track this down but I suspect it may be related to https://github.com/bazelbuild/rules_closure/pull/347, but it's not so easy to bisect it.

Any ideas?

Reproduce the Bazel compilation of the generated protobuf JavaScript file and inspect pb.i.js around line 2076, where the duplicate namespace is reported. Review the suppress configuration and compare its handling with rules_closure PR #347. Done means identifying why JSC_DUPLICATE_NAMESPACE is rejected and establishing the supported way to handle the diagnostic.

Written by the indexing model from the issue text.