Add jpql nullif serializer

[waveofmymind]

Motivation:

Modifications:

• Implement JpqlNullIfSerializer

Commit Convention Rule

• Please commit your modification based by conventional commit
• This commit convention is referred from angular convention

Commit type	Description
feat	New Feature
fix	Fix bug
docs	Documentation only changed
ci	Change CI configuration
refactor	Not a bug fix or add feature, just refactoring code
test	Add Test case or fix wrong test case
style	Only change the code style(ex. white-space, formatting)
chore	It refers to minor tasks such as library version upgrade, typo correction, etc.

• If you want to add some more commit type please describe it on the Pull Request

Result:

Close #347

[CLAassistant]

All committers have signed the CLA.

[shouwn]

Your first contribution will be greatly appreciated.