IDEMPIERE-6125 Allow monitoring null transactions on idempiereMonitor

[CarlosRuiz-globalqss]

https://idempiere.atlassian.net/browse/IDEMPIERE-6125

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.
• I have checked my code and corrected any misspellings
• In hard-to-understand areas, I have commented my code.
• My changes generate no new warnings

Tests

• I have tested the direct scenario that my code is solving
• I checked all collaterals that can be affected by my changes, and tested other potential affected scenarios
• 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

Documentation

• I have made corresponding changes to the documentation as follows:
• • 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]

looks good