Repo 2 - outbound HTTP connection leak and broken not found cache when optional npm abbreviated metadata feature is enabled

Using 2.15.0 or 2.15.1, enable abbreviated npm metadata feature by adding this line to conf/nexus.properties:

nexus.npm.abbreviateMetadata=true

Create a proxy repo to official npm registry at https://registry.npmjs.org

Make more than 20 requests for a package that does not exist:

#!/bin/bash

for index in {1..40}; do
  curl -H "Accept: application/vnd.npm.install-v1+json; q=1.0, application/json; q=0.8, */*"  "http://localhost:8081/nexus/content/repositories/npm-proxy/@example%2Fdoes-not-exist" -s -w "%{stderr} %{http_code}\n" 1>/dev/null; 
done

Two problems are noticed:

1. The outbound http connection pool for the specific proxy repo gets filled and leaks http connections after 20 connections are used.
2. Even though the remote returns 404 responses, these are never cached despite the fact that the not found cache is enabled and set to 1440 minutes.

Expected

Do not leak http connections when the abbreviated metadata feature is enabled. Properly cache 404 responses.