Can't find resource for bundle java.util.PropertyResourceBundle

Problem: Something went wrong while creating User UDF which results in below error on OIM UI page.

Effect of error on OIM UI :

1. Cannot create the user from UI.
2. Cannot search all users or specific users.
3. The sysadmin console doesn't respond and is blank.

Solution: 

1. Export User.xml.
2. Now open the User.xml file using any text editor and remove the UDF which you have created.
3. Again import the modified file import export functionality.

[Note: For Export and Import use Export-Import functionality.]