Remove the null check, fix issue #1755

[xuzhg]

Issues

This pull request fixes issue https://github.com/OData/odata.net/issues/1755.

#2281

Description

• SelectExpandBinder generates the "Null" expression can't work for "EntityFramework6".

IsNull = .If ($$it == null) {
            null
        } .Else {
            $$it.Description
        } == null

However, it seems we don't need the "IsNull" check for the complex. So, let's remove this.

Checklist (Uncheck if it is not completed)

• Test cases added
• Build and test with one-click build and test script passed

Additional work necessary

If documentation update is needed, please add "Docs Needed" label to the issue and provide details about the required document change in the issue.

[mikepizzo]

Do we know why this was added originally? Is this needed for proper null propagation for other data sources?

Can you re-run the tests to verify no breaking changes? It looks like there was a problem executing the CI.

[xuzhg]

I checked with "Smit Patel", and the changes here looks good to him. So, I'd merge it