Helm virtual fails to merge Helm remote index

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ISSUE

Helm install of a remote helm package fails because index.yaml from virtual helm does not contain index from helm remote. Debug logs show that virtual index failed to merge-in the remote index.

STEPS TO REPRODUCE:
1.Setup 5.8.9
2. Setup helm virtual
3. download index.yaml via virtual helm repo (e.g. wget http://$ARTIFACTORY_URL/artifactory/helm/index.yaml)

It doesn't reproduce in 6.0.3

LOGS

0180702204423|878|REQUEST|RESTRICTED_URL|admin|GET|/helm/index.yaml|HTTP/1.0|200|51
20180702204431|12|REQUEST|RESTRICTED_URL|admin|GET|/helm/index.yaml|HTTP/1.0|200|51

2018-07-02 21:27:09,801 [http-nio-8081-exec-3] [DEBUG] (o.a.a.h.r.i.HelmVirtualInterceptor:53) - Triggering url-based Helm index file in virtual repo helm for index.yaml

2018-07-02 21:27:09,804 [art-exec-1454] [DEBUG] (o.a.a.h.HelmServiceImpl:104) - Sync Virtual url Helm calculation for helm:index.yaml

2018-07-02 21:27:09,804 [art-exec-1454] [DEBUG] (o.a.a.h.HelmServiceImpl:147) - Starting virtual Helm metadata calculation for path helm/index.yaml per RESTRICTED_URL

2018-07-02 21:27:09,805 [art-exec-1454] [DEBUG] (o.a.a.h.HelmServiceImpl:154) - Checking if custom index already exists at: helm:.index/814994902/index.yaml

2018-07-02 21:27:09,807 [art-exec-1454] [DEBUG] (o.a.a.h.HelmServiceImpl:175) - Merging Helm repositories for helm

2018-07-02 21:27:09,974 [art-exec-1454] [INFO ] (o.a.r.HttpRepo      :414) - helm-remote downloading https://storage.googleapis.com/kubernetes-charts/index.yaml 2.04 MB

2018-07-02 21:27:10,250 [art-exec-1454] [INFO ] (o.a.r.HttpRepo      :427) - helm-remote downloaded  https://storage.googleapis.com/kubernetes-charts/index.yaml 2.04 MB at 7,655.83 KB/sec

2018-07-02 21:27:10,268 [art-exec-1454] [ERROR] (o.a.a.h.r.m.HelmVirtualMerger:194) - Couldn't read index file in remote repository helm-remote : (was com.github.zafarkhaja.semver.UnexpectedCharacterException) (through reference chain: org.jfrog.repomd.helm.model.HelmIndexYamlMetadata["entries"]>java.util.LinkedHashMap["cert-manager"]>java.util.TreeSet[0])

2018-07-02 21:27:10,277 [art-exec-1454] [DEBUG] (o.a.a.h.r.m.HelmVirtualMerger:195) - Couldn't read index file in remote repository helm-remote

com.fasterxml.jackson.databind.JsonMappingException: (was com.github.zafarkhaja.semver.UnexpectedCharacterException) (through reference chain: org.jfrog.repomd.helm.model.HelmIndexYamlMetadata["entries"]>java.util.LinkedHashMap["cert-manager"]>java.util.TreeSet[0])