npm package metadata dist-tags section can be empty when merged from a group repository member group repository

Reproduce

Create this type of NPM format repository structure:

npm (group)
|
|-- npm-hosted (group)
|   |
|   |-- npm-releases (hosted)
|   |
|   `-- npm-snapshots (hosted)
|
`-- npm-proxy-npmjs (proxy, official registry)

Then follow these instructions:

1. create a scoped package @test/some-package with version 1.0.0-rc.1
2. publish this package to the npm-releases repository with

   npm publish

3. in a different directory create the same scoped package with a different version 1.0.0-rc.1-20200601210614
4. publish this package to the npm-snapshots repository with

   npm publish

5. in another directory try to list the dist tags for @test/some-package when logged into the npm group repository:

   npm dist-tag ls @test/some-package
   npm ERR! dist-tag ls Couldn't get dist-tag data for Result {
   npm ERR! dist-tag ls   type: 'tag',
   npm ERR! dist-tag ls   registry: true,
   npm ERR! dist-tag ls   where: undefined,
   npm ERR! dist-tag ls   raw: '@test/some-package',
   npm ERR! dist-tag ls   name: '@test/some-package',
   npm ERR! dist-tag ls   escapedName: '@test%2fsome-package',
   npm ERR! dist-tag ls   scope: '@test',
   npm ERR! dist-tag ls   rawSpec: '',
   npm ERR! dist-tag ls   saveSpec: null,
   npm ERR! dist-tag ls   fetchSpec: 'latest',
   npm ERR! dist-tag ls   gitRange: undefined,
   npm ERR! dist-tag ls   gitCommittish: undefined,
   npm ERR! dist-tag ls   hosted: undefined
   npm ERR! dist-tag ls }
   npm ERR! code E500
   npm ERR! 500 javax.servlet.ServletException: java.lang.ClassCastException: org.sonatype.nexus.repository.view.payloads.BytesPayload cannot be cast to org.sonatype.nexus.repository.view.Content - GET http://127.0.0.1:8081/repository/npm/-/package/@test%2fsome-package/dist-tags
   

The stack trace of the exception being thrown is:

java.lang.ClassCastException: org.sonatype.nexus.repository.view.payloads.BytesPayload cannot be cast to org.sonatype.nexus.repository.view.Content
at org.sonatype.nexus.repository.npm.internal.NpmFacetUtils.lambda$7(NpmFacetUtils.java:566)
at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
at java.util.Iterator.forEachRemaining(Iterator.java:116)
at java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)
at org.sonatype.nexus.repository.npm.internal.NpmFacetUtils.mergeDistTagResponse(NpmFacetUtils.java:570)
at org.sonatype.nexus.repository.npm.internal.NpmFacetUtils$mergeDistTagResponse.call(Unknown Source)
at org.sonatype.nexus.repository.npm.internal.NpmGroupDistTagsHandler.doGet(NpmGroupDistTagsHandler.groovy:55)
at org.sonatype.nexus.repository.group.GroupHandler.handle(GroupHandler.java:95)

Expected

• npm dist-tags command should not get 500 response
• npm install commands which rely on dist-tags being non-empty to resolve packages should not fail to resolve the expected versions
• avoid ClassCastException