NPE when editing an issue

When attempting to edit an issue, I get the following:

java.lang.NullPointerException
at com.atlassian.jira.web.action.issue.EditIssue.doDefault(EditIssue.java:66)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:324)
at webwork.action.ActionSupport.invokeCommand(ActionSupport.java:337)
at webwork.action.ActionSupport.execute(ActionSupport.java:73)
at webwork.dispatcher.ServletDispatcher.service(ServletDispatcher.java:185)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:336)
at com.evermind[Orion/1.5.4 (build 10585)]._ie.doFilter(.:59)
at com.opensymphony.module.sitemesh.filter.PageFilter.parsePage(PageFilter.java:124)
at com.opensymphony.module.sitemesh.filter.PageFilter.doFilter(PageFilter.java:68)
at com.evermind[Orion/1.5.4 (build 10585)]._ic.doFilter(.:16)
at com.atlassian.jira.web.security.SecurityFilter.doFilter(SecurityFilter.java:201)
at com.evermind[Orion/1.5.4 (build 10585)]._ic.doFilter(.:20)
at com.atlassian.jira.web.security.LoginFilter.doFilter(LoginFilter.java:189)
at com.evermind[Orion/1.5.4 (build 10585)]._deb._lnc(.:376)
at com.evermind[Orion/1.5.4 (build 10585)]._deb._wmb(.:170)
at com.evermind[Orion/1.5.4 (build 10585)]._co._wbb(.:581)
at com.evermind[Orion/1.5.4 (build 10585)]._co._fs(.:189)
at com.evermind[Orion/1.5.4 (build 10585)]._bt.run(.:62)