Query.NullHandlingOnOrder does not work on SQLserver

When testing with SQLServer, we found that `Query.NullHandlingOnOrder` contsructs queries in flowable that cannot be executed by MS SQLserver. I am not sure if I should post this as a bug report to mybatis instead?

The corresponding stacktrace can be found here: https://gist.github.com/mlippens/3689a43228e3f86422b160e324efcbcc

As for the version of mssql, we use the docker linux image https://hub.docker.com/r/microsoft/mssql-server-linux/, but we could also reproduce it with an actual install of SQLServer.

Start with Query.NullHandlingOnOrder and reproduce the reported query against SQL Server, using the stacktrace at the linked Gist as the initial diagnostic reference. Done means the query generated for null handling in ordering executes successfully on SQL Server.

Scritto dal modello di indicizzazione a partire dal testo della issue.