Duplicate check for referrals submitted by agencies

Summary: Ability to restrict agent to refer candidate already present in candidate database

Content (required):

This is with respect to an issue which is faced where system is allowing agent to refer a candidate which is already present in candidate database.

We want to restrict the candidate to be referred by agency if that same candiadte is already present in the candidate database but system is not allowing me to do the same.

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):