[Bug][DataHub] getDocument on a document folder fails: "Abstract type Document must resolve to an Object type at runtime"

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Affected Version

2026.2

Affected capability

DataHub

Steps to reproduce

1. Pimcore 2026.2 with pimcore/data-hub, a GraphQL endpoint configured with the Document schema enabled.
2. Create a document folder, e.g. /shared.
3. Query that folder by its full path:

{
  getDocument(fullpath: "/shared") {
    ... on document_folder {
      id
      fullpath
    }
  }
}

The same happens whenever a document folder is reached through a relation, a document/object property or an editable relation (AnyDocumentTarget / AnyTarget).

Actual Behavior

The query fails at runtime:

Abstract type Document must resolve to an Object type at runtime for field Query.getDocument ... received null

DocumentType::resolveType() has no branch for Document\Folder and returns null, and _document_folder — although it is a registered type — is not a member of the document union returned by DocumentType::getTypes(). So the union can neither resolve nor accept a document folder.

For object folders the equivalent case already works (_object_folder); only documents are affected.

Expected Behavior

getDocument() on a folder path returns the folder as document_folder, and document folders reached through relations/properties resolve to the registered _document_folder type. Non-folder documents stay unaffected.

Additional notes

Fix is prepared in pimcore/data-hub#1126 (adds _document_folder to the document union and resolves Document\Folder to it; includes a regression test). It complements the resolveType() folder guards merged with pimcore/data-hub#1105 — both halves are needed for the document-folder case.

This issue is created as the tracking issue required by the issue-link guardrail for that PR.