Code Review: Refactor code with new method

[kattsky]

No description provided.

[kattsky]

Hi Ravi, as the Issue tab is unavailable in the repo, I've decided to add comments in your CONTRIBUTING.md file for the code review.
Then I forked your repo and raised a PR as a workaround.

Great work with addressing the problem in your code.
Maybe for a little bit of enhancement to make the code more readable and robust, you could consider introducing a method called DeserializeNonNullValues(JsonData jsonData) to extract non-null values from JSON data. Then returns a 'Student' object that has just non-null values.

This will help simplify the logic in Main method. Plus, it conforms to the principle of encapsulation.
Let me know your thoughts. Great work, Ravi.