Check for null owner in AddUnits

[trevan]

Fixes #7226

I don't know the null owner occurred. But there exists code that already checks for the null owner case so this adds similar code to the AddUnits class.

Functional Changes

[] New map or map update
[] New Feature
[] Feature update or enhancement
[] Feature Removal
[] Code Cleanup or refactor
[] Configuration Change
[x] Problem fix
[] Other:

Testing

I don't know how to duplicate the null owner case so I just ensured that things continued to work as expected.

Screens Shots

Additional Notes to Reviewer

Release Note

FIX|Fix null error in AddUnits#buildUnitOwnerMap when loading a saved game

[trevan]

I wasn't sure how to give a user friendly release note since I'm not sure when this happens.. And the user just sees a "Error: null" error which can happen in lots of situations so I can't say that I fixed that error.

[DanVanAtta]

Did you play test this @trevan to see what happens? You can hack up the code to always return null for owners and then just see how the game plays out.

I think the problem comes up from serialization, objects are not instantiated via their constructors and so who knows what can happen...

If we go with this workaround, would such units cause problems in the save game - is the save game just corrupt or is this a valid work-around?

[trevan]

Did you play test this @trevan to see what happens? You can hack up the code to always return null for owners and then just see how the game plays out.

I think the problem comes up from serialization, objects are not instantiated via their constructors and so who knows what can happen...

If we go with this workaround, would such units cause problems in the save game - is the save game just corrupt or is this a valid work-around?

I tested it but I don't know how to get a null owner. Returning null for getOwner actually breaks a lot of things. I can't play most of my saves. I noticed, though, that in Unit#setOwner, it will use the NULL_PLAYERID if the owner is null. So I'm going to set that as the owner instead of null.

[DanVanAtta]

I think/suspect the null_playerid indicates neutrals. You might get some interesting behavior 😁