VHost httpContext returned null for empty httpContext in Oracle DB

[chamilaadhi]

There is an inconsistency in the payload returned when a new Gateway Environments is created with Oracle DB. When a new Gateway Environments is created without providing an Https context under 'Advanced settings', null is returned for oracle DB. An empty string is sent for other DB types

This is captured with EnvironmentTestCase test case

Steps to reproduce

1. Configure APIM 4.0 with Oracle DB
2. Log in to admin portal and create a new gateway environment (Don't set any under 'Advanced settings' )
3. Check the response. You would see httpContext sent as null. (This is returned as "" on other DBs)
4. Check environment listing as well and you could see httpContext sent as null here as well. (This listing is tested in EnvironmentTestCase test case)

Fix Return empty string instead of null