Eclipse 2025-09 - NPE in Background Indexer Crash Recovery - "onDisk.categoryTables" is null

Just saw this in my Error Log:

I have no idea how to reproduce it, just saw it the first time and thought I report it.

```
java.lang.NullPointerException: Cannot invoke "org.eclipse.jdt.internal.compiler.util.HashtableOfObject.put(char[], Object)" because "onDisk.categoryTables" is null
at org.eclipse.jdt.internal.core.index.DiskIndex.mergeCategory(DiskIndex.java:526)
at org.eclipse.jdt.internal.core.index.DiskIndex.mergeCategories(DiskIndex.java:481)
at org.eclipse.jdt.internal.core.index.DiskIndex.mergeWith(DiskIndex.java:582)
at org.eclipse.jdt.internal.core.index.Index.save(Index.java:229)
at org.eclipse.jdt.internal.core.index.MetaIndex.save(MetaIndex.java:98)
at org.eclipse.jdt.internal.core.search.indexing.IndexManager.saveMetaIndex(IndexManager.java:1227)
at org.eclipse.jdt.internal.core.search.indexing.IndexManager.saveIndexes(IndexManager.java:1203)
at org.eclipse.jdt.internal.core.search.indexing.IndexManager.notifyIdle(IndexManager.java:822)
at org.eclipse.jdt.internal.core.search.processing.JobManager.indexerLoop(JobManager.java:508)
at java.base/java.lang.Thread.run(Thread.java:1583)

```

```
eclipse.buildId=4.37.0.20250905-1455
java.version=21.0.9
java.vendor=Eclipse Adoptium
BootLoader constants: OS=macosx, ARCH=aarch64, WS=cocoa, NL=de_DE
Framework arguments: -product org.eclipse.epp.package.committers.product -keyring /Users/me/.eclipse_keyring
Command-line arguments: -os macosx -ws cocoa -arch aarch64 -product org.eclipse.epp.package.committers.product -keyring /Users/me/.eclipse_keyring

This is a continuation of log file /Users/me/eclipse-workspace/.metadata/.bak_8.log
Created Time: 2025-11-12 23:31:05.954

```

Maybe related / similar error:
- https://github.com/eclipse-jdt/eclipse.jdt.core/issues/235
- https://github.com/eclipse-jdt/eclipse.jdt.core/issues/1154#issuecomment-1596509618