Accept a String vertex id in IndexSerializer.removeElement (#4928)

[batrived]

Fixes #4928.

IndexSerializer.removeElement rejected every vertex id which is not a Long, but the very next line calls element2String, which accepts a Long, a RelationIdentifier or a String. The two methods disagreed about what a valid element id is, and the stricter of them ran first.

A graph configured with graph.allow-custom-vid-types assigns String vertex ids. The only caller is StandardTransactionLogProcessor, which calls removeElement when the element of a restored transaction no longer exists. So recovering a transaction that deleted an indexed vertex threw IllegalArgumentException, the stale index document was never removed, and the recovery mechanism that exists to repair a diverged index could not complete.

This applies the fix suggested in the issue: accept the same vertex ids element2String accepts. A relation index still requires a RelationIdentifier.

Testing

IndexSerializerRemoveElementTest covers a String vertex id, a Long vertex id, a relation id, and the ids that must still be rejected. I confirmed the String case reproduces the reported failure without the fix:

IllegalArgument Invalid element id [customVertexId] provided for index: Mock for MixedIndexType

Each test also asserts the resulting document id round-trips back to the original element id through string2ElementId, so the document that gets removed is the right one, and that the entry list is empty, which is how a document removal is expressed.

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[Copilot]

Pull request overview

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Updates IndexSerializer.removeElement to accept String vertex IDs (in addition to Long) to support graphs configured with custom vertex ID types, and adds unit tests to validate accepted and rejected ID/category combinations.

Changes:

• Allow String IDs when removing vertex documents from mixed indexes.
• Add unit tests covering String vertex IDs, Long vertex IDs, relation IDs, and invalid ID/category combinations.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
janusgraph-core/src/main/java/org/janusgraph/graphdb/database/IndexSerializer.java	Expands vertex ID validation in removeElement to accept String IDs.
janusgraph-core/src/test/java/org/janusgraph/graphdb/database/IndexSerializerRemoveElementTest.java	Adds regression/unit tests for removeElement ID handling and document-id roundtrip behavior.

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