Spring Add a PropertyEditor that convert to null for empty string

Issue: SPR-13561

For details, refer to the SPR-13561. I have signed and agree to the terms of the SpringSource Individual Contributor License Agreement.

Comment From: snicoll

@kazuki43zoo thanks for the PR and sorry it took so long to get back to you. Looking at the issue history, this request didn't get a lot of traction from the community and was closed. I am going to close this PR as well.