Can't access or create review due to non-existent/deleted users in group

2013-07-16 07:51:18,221 ERROR - Exception "javax.servlet.ServletException: javax.servlet.jsp.JspException: javax.el.ELException: Problems calling function 'crev:showJoinReview'" (javax.servlet.ServletException) while processing "/source/cru/CR-5" (Referer:"https://localhost:8060/source/")
javax.servlet.ServletException: javax.servlet.ServletException: javax.servlet.jsp.JspException: javax.el.ELException: Problems calling function 'crev:showJoinReview'
        at com.opensymphony.webwork.dispatcher.DispatcherUtils.serviceAction(DispatcherUtils.java:285)
        at com.opensymphony.webwork.dispatcher.ServletDispatcher.service(ServletDispatcher.java:111)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:848)
        at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:669)
        at org.eclipse.jetty.servlet.ServletHandler$Chain.doFilter(ServletHandler.java:1526)
        at com.atlassian.plugin.servlet.filter.IteratingFilterChain.doFilter(IteratingFilterChain.java:46)
...
Caused by: javax.servlet.ServletException: javax.servlet.jsp.JspException: javax.el.ELException: Problems calling function 'crev:showJoinReview'
...
Caused by: javax.servlet.jsp.JspException: javax.el.ELException: Problems calling function 'crev:showJoinReview'
...
Caused by: javax.el.ELException: Problems calling function 'crev:showJoinReview'
...
Caused by: java.lang.NullPointerException
        at com.cenqua.crucible.model.managers.CrucibleUserManager$1.compare(CrucibleUserManager.java:95)
        at com.cenqua.crucible.model.managers.CrucibleUserManager$1.compare(CrucibleUserManager.java:93)
        at java.util.TimSort.countRunAndMakeAscending(TimSort.java:324)
        at java.util.TimSort.sort(TimSort.java:203)
        at java.util.TimSort.sort(TimSort.java:173)
        at java.util.Arrays.sort(Arrays.java:659)
        at java.util.Collections.sort(Collections.java:217)
        at com.cenqua.crucible.model.managers.CrucibleUserManager.usernamesToUsers(CrucibleUserManager.java:93)
        at com.cenqua.crucible.model.managers.CrucibleUserManager.getGroupOfUsers(CrucibleUserManager.java:106)
        at com.cenqua.crucible.model.Project.getAllowedReviewers(Project.java:114)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)