ID 547518 - In Katana when using the Geolib3-Mt (Experimental) geolibRuntime with opTreeOptmizations On, merging two empty GroupStack nodes causes any subsequent Renders to fail, if this merge occurs on the left most input of your node graph

1.  Open Katana and recreate the following Node Graph tree:

1. 
   

   

 
2.  Set the Edit Flag on to the RenderSettings node and in the Parameters tab, change the geolibRuntime parameter to Geolib3-Mt (Experimental).

3.  Now under the sceneTraversal group parameter, set verboseLogging to On.

4.  Start a Preview Render, this can be done by pressing Ctrl + P.

5.  Navigate to the Render Log tab.

Expected behaviour
The Render completes as expected.
 
Actual behaviour
The Render fails when running the 'FlattenMergeHierarchies' pass.
 
Workaround
Either fill the GroupStack/GroupMerge node with a node, or move a non empty merge left of the empty merge.
 
Reproduced by support
This bug has been reproduced in:
Katana 6.0v2 - Windows 10, CentOs 7
Katana 5.0v1 - Windows 10, CentOs 7
Katana 4.5v1 -  Windows 10, CentOs 7
 
Earliest version tested
Katana 4.5v1 - This feature did not exist before this version.