DO NOT MERGE: Defect fixes for sprint Spectre

Background
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This pull request fixes the following defects:

* [MAGN-3166](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-3166) Undo deletion of List.Join crashes Dynamo

Unit Tests
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* Unit test case ```Defect_MAGN_3166``` added to verify the fix
* More to come...