Fix logic behind eSourcingDisplay message

Is it worth combining both and having an "is null or empty" check here - i.e. 
if (supplierDetails.get("esourcingId") == "null" || supplierDetails.get("esourcingId").size() == 0) {....

The eSourcing banner seems to be showing OK on lIve at the moment with the size == 0 check (logged in as the DM Supplier team that we are all on), so not sure why this is a problem.