ParameterNamesCodeMiningTest failed in CI job

See: https://github.com/eclipse-jdt/eclipse.jdt.ui/pull/3074/checks?check_run_id=86313496662

```
org.opentest4j.AssertionFailedError: expected: but was:
at org.junit.jupiter.api.AssertionFailureBuilder.build(AssertionFailureBuilder.java:151)
at org.junit.jupiter.api.AssertionFailureBuilder.buildAndThrow(AssertionFailureBuilder.java:132)
at org.junit.jupiter.api.AssertNull.failNotNull(AssertNull.java:50)
at org.junit.jupiter.api.AssertNull.assertNull(AssertNull.java:35)
at org.junit.jupiter.api.AssertNull.assertNull(AssertNull.java:30)
at org.junit.jupiter.api.Assertions.assertNull(Assertions.java:279)
at org.eclipse.jdt.text.tests.codemining.ParameterNamesCodeMiningTest.testCollapsedFolding(ParameterNamesCodeMiningTest.java:235)
at java.base/java.lang.reflect.Method.invoke(Method.java:580)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)

```

Start with ParameterNamesCodeMiningTest.testCollapsedFolding at line 235 and the linked CI check. Reproduce the failure and trace the delayed reconciler's null preference store; done means the test completes without the internal error and the assertion passes.

Written by the indexing model from the issue text.