Correctly catch potentially null value

[inanemed]

check if referenceDatabase not null instead of referenceSnapshot.

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Dev Handoff Notes (Internal Use)

Links

• Stand alone PR
• Test Results: https://github.com/liquibase/liquibase/pull/2330/checks

Testing

• Steps to Reproduce: Not sure. The fix obviously avoids a nulls a null pointer which could happen, but I'm not sure how to set up something naturally happening in liquibase to trigger it. Not sure what could lead to a null value, but if anything does it will handle it better now. Probably needs no additional manual testing?
• Guidance:
  • Impact: Stops potential null pointer

Dev Verification

Reviewed code.

[nvoxland]

Thanks. referenceDatabase gets called in the if statement, so checkign that it is null and not referenceSnapshot is what's neede.

[XDelphiGrl]

I reviewed the changes in the commit and agree, @nvoxland, that there is nothing additional to test from a QA perspective. Should there be a unit test for this change?

All automated tests passed.
No new tests required.
No manual testing required.
Passing Funcitonal Tests

[nvoxland]

@XDelphiGrl I think probably not a useful enough unit test. The code is trying to do a lot of things there, and a lot of it is around how it's interacting with the outside systems and the coordination between components.

I'd like to eventually be able to refactor that code to have a better separation between what we'd test as a unit and what takes integration/coordination tests. But since we don't want to get into that right now for this change, I think the existing tests cover it well enough even if they are a bit slower to test it.

[XDelphiGrl]

@nvoxland, thank you for taking a look at adding a test; makes sense to skip since it would add little value. Moving to ready to merge.