Fix the remaining issues for MAGN-3785
Fix MAGN-3218 Walls created on first run are not cleaned up
Add a null check.
Check ref point is valid before rendering.
Merge pull request #1867 from Randy-Ma/magn-3218

Fix MAGN-3218 Walls created on first run are not cleaned up
Merge pull request #1855 from Randy-Ma/master

Fix the remaining issues for MAGN-3785
Merge branch 'master' of https://github.com/DynamoDS/Dynamo into imperativeNodeCompare