[BUG] Fix Nested Fields when Derived Sources are enabled

[akash-shankaran]

What is the bug?
Today, we are disabling the use of nested fields when derived sources are enabled as this results in an exception. #312 (comment)

Fix the issue, and the associated test DerivedSourceIT. testNestedField

How can one reproduce the bug?
Steps to reproduce the behavior:

1. Remove the try-catch block from the above test.
2. Remove the exception from DerivedSourceVectorTransformer.java, and uncomment the TODO line c1863ce
3. See error

What is the expected behavior?
Derived sources with nested fields should work, and the retrieved document should match what is provided in the test.

What is your host/environment?

• OS: [e.g. iOS]
• Version [e.g. 22]
• Plugins

Do you have any screenshots?
If applicable, add screenshots to help explain your problem.

Do you have any additional context?
Add any other context about the problem.

[akash-shankaran]

@kush992 , @WojciechKrakowiak - please feel free to tackle this between your team when you have bandwidth.

[WojciechKrakowiak]

Sure, we'll pick it up soon

[ergunkezer1]

I will work on this