How to create index for Column Table in SAP Hana?

I have a little problem in create a index for a column table in sap hana. I need to create index and the value maybe could be null.

In Oracle SQL I create like this:

CREATE INDEX IDX_MY_INDEX ON MY_TABLE (NVL(MY_COLUMN,' ')); 

But in the Sap Hana, I don't know what can replace the nvl function.

Can you help me?

Message was edited by: Tom Flanagan