Author mapping is failing with NPE

Author mapping is failing with NPE when trying to add a mapping to a user and the same mapping is already defined for an inactive user.

Caused by: java.lang.NullPointerException
	at com.cenqua.fisheye.web.profile.actions.EditAuthorMappingAction.editMapping(EditAuthorMappingAction.java:171)

Workaround: manually remove the mapping for the inactive user via the administration panel: Admin / User Settings / User Mappings