IDEMPIERE-5645 - fix NPE on report Script columns

[PeterTakacs300]

Reopened JIRA ticket: https://idempiere.atlassian.net/browse/IDEMPIERE-5645

Pull Request Checklist

• My code follows the code guidelines of this project
• My code follows the best practices of this project
• I have performed a self-review of my own code
• My code is easy to understand and review.
• In hard-to-understand areas, I have commented my code.
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes
• I have added unit tests that prove my fix is effective or that my feature works
• Any dependent changes have been merged and published in downstream modules
• I have checked my code and corrected any misspellings
• I have made corresponding changes to the documentation as follows:
  • New feature (non-breaking change which adds functionality): I have created the New Feature page in the project wiki explaining the functionality and how to use it. If relevant, I have committed sample data to the core seed to have usable examples in GardenWorld.
  • Breaking change (fix or feature that would cause existing functionality to not work as expected): I have documented the change in a clear way that everyone in the community can understand the impact of the change.
  • Improvement (improves and existing functionality): This documentation is needed if the improvement changes the way the user interacts with the system or the outcome of a process/task changes. If it is just, for instance, a performance improvement, documentation might not be needed.
• The changed/added documentation is in the project wiki (not privately-hosted pdf files or links pointing to a company website) and is complete and self-explanatory.

[hengsin]

trivial fix, good to go