InMemorySetState.retract NPEs on an absent secondary-index key in MEMORY-cache lookup join

[LuciferYang]

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Paimon version

master (1.5-SNAPSHOT)

Compute Engine

Flink (secondary-index lookup join with lookup.cache = MEMORY).

Minimal reproduce step

1. Run a lookup join whose join key is not the table's primary key (a secondary-index lookup), with lookup.cache = MEMORY and a lookup filter (predicate).
2. Feed a changelog where a row that does not pass the predicate is later deleted (a -D / -U for that key).

What doesn't meet your expectations?

The lookup refresh crashes with a NullPointerException. SecondaryIndexLookupTable.refreshRow only adds a row to the index state when the predicate passes (on +I / +U), but retracts unconditionally on -D / -U. So a row that was filtered out was never added, and its later retract reaches InMemorySetState.retract, which does values.get(secKey).remove(...) with no null check and throws. The disk-backed sibling LocalKvSetState.retract already treats an absent key as a no-op, so the same join crashes only in MEMORY cache mode.

Anything else?

This is a behavior inconsistency between the two SetState implementations; MEMORY mode should tolerate the absent-key retract like the disk-backed one.

Are you willing to submit a PR?

• I'm willing to submit a PR!