Fix for empty grain response deseriaslized to null

[Ivanvv]

Description

Bug: when a grain responses with empty class or class containing all default data, it will be deserialized to 'null' on the receiving end.
After fix - it will be deserialized to empty class

Purpose

This pull request is a:

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[CLAassistant]

All committers have signed the CLA.