JIRA allows users to be created with line breaks through the JIRA Importers Plugin (and possibly other plugins), but does not handle these users correctly.

Steps to replicate:

1. Import a user, containing a line break in the username, through the CSV importer (JIM-1001);
2. Try to edit or delete these users.

Expected Behavior:

The administrator would be able to edit or delete the broken users.

Actual Behavior:

It is not possible to edit or delete this user. The following appears on the logs:

2013-07-01 17:20:32,465 http-bio-8090-exec-4 ERROR      [500ErrorPage.jsp] Exception caught in 500 page null
java.lang.NullPointerException
	at com.atlassian.jira.web.action.admin.user.EditUser.buildNewUser(EditUser.java:106)
	at com.atlassian.jira.web.action.admin.user.EditUser.doValidation(EditUser.java:57)
	at webwork.action.ActionSupport.validate(ActionSupport.java:391)
...

Workaround:

1. Create a backup of JIRA;
2. Unzip the backup;
3. Open the XML backups in a text editor;
4. Use the 'Find and Replace' feature of the text editor to replace e.g. 'Matheus
   Fernandes' with 'matheusfernandes';
5. Save the files, zip them together again;
6. And re-import the backup.
   ^{Reference: 'User does not exist' error when trying to use, edit or delete an user}