Add defensive null check to stop null pointer exception

[Mustard]

When joining tables (entities) that have a @customizer (history policy) eclipselink will throw a NullPointerException

I have a simple proof of concept project that demonstrates the issue. Ideally this could be added to the eclipselink project as a test, any help around where to add this test in the project would be appreciated as I couldn't even get the 2.7 branch to build locally and am unfamiliar with the project

This pull request would resolve this issue https://bugs.eclipse.org/bugs/show_bug.cgi?id=526836

A possible other solution / improvement might be to initialise asOfClause in org.eclipse.persistence.internal.expressions.DataExpression such that it is not null in the first place

protected AsOfClause asOfClause = AsOfClause.NO_CLAUSE;

I have agreed to the Eclipse Contributor Agreement https://www.eclipse.org/user/mustard

[lukasj]

wrt test - take a look at jpa/eclipselink.jpa.testapps and try to find an existing test this could be added to - jpa.test.advanced or jpa.test.jpql look like good candidates; it does not make much sense to add whole new project for this

[Mustard]

Hi @lukasj

Thanks for your help!

Took me a while to get back to it but I have added tests to the pull request, if there is anything else I can do to move this along let me know

[lukasj]

at the time of submission, ECA was valid

[robertpatrick]

@arjantijms I reproduced the original problem and a new regression using current 5.x code with the PR’s production changes:

Test	Current master	Full PR change	Two null guards only
Prepare the reported join	NPE	Pass	Pass
Historical joined query	Past parent + past child	Past parent + current child	Past parent + past child

The problem is the new AsOfClause.NO_CLAUSE initializer. Previously, null allowed a child expression to inherit its parent’s historical timestamp. NO_CLAUSE prevents that inheritance, silently mixing historical and current data.

What the author should do:

1. Remove that initializer, retaining the two targeted null guards—the narrower variant passed both local tests.
2. Add a historical-join result test and close the test’s EntityManager. The existing preparation test is meaningful and correctly registered.
3. Refresh onto master and obtain clean CI, including the existing tests affected by adding history policies to Room/Door.