Epic sidebar does not display ancestor epics

Issue / Bug

There is a bug in the issuable apollo client's caching configuration:

// app/assets/javascripts/graphql_shared/issuable_client.js#161

      EpicConnection: {
        merge(existing = { nodes: [] }, incoming, { args }) {
          if (!args.after) { // Problematic line.

args may be null and the check should be !args?.after.

To identify the parent of the epic, we can use the following workarounds:

Workarounds

Workaround 1 (graphql endpoint)

https://gitlab.com/-/graphql-explorer

query epicParent($fullPath: ID!, $iid: ID) {
  workspace: group(fullPath: $fullPath) {
    issuable: epic(iid: $iid) {
      parent{
        webUrl
      }
    }
  }
}

{
  "fullPath": "gitlab-org",
  "iid": 10996
}

Workaround 2

The system notes can also be followed, example: Dov Hershkovitch added to epic &9888 7 months ago