We have been having notification problems from the Issue tracker. I've been able to reproduce the problem by impersonating a user and submitting an issue without assigning it to an individual. No error occurs on the initial submission but when the issue is updated and assigned, the following error appears in labkey-error.log.

ERROR IssuesController 2009-10-30 10:16:40,568 http-8443-Processor13 : sendUpdateEmail
java.lang.NullPointerException
    at org.labkey.issue.IssuesController.getEmailAddresses(IssuesController.java:1116)
    at org.labkey.issue.IssuesController.sendUpdateEmail(IssuesController.java:1077)
    at org.labkey.issue.IssuesController.access$2700(IssuesController.java:59)
    at org.labkey.issue.IssuesController$IssueUpdateAction.handlePost(IssuesController.java:633)
    at org.labkey.issue.IssuesController$IssueUpdateAction.handlePost(IssuesController.java:575)
    at org.labkey.api.action.FormViewAction.handleRequest(FormViewAction.java:91)
    at org.labkey.api.action.FormViewAction.handleRequest(FormViewAction.java:75)
    at org.labkey.api.action.BaseViewAction.handleRequestInternal(BaseViewAction.java:167)
    at org.springframework.web.servlet.mvc.AbstractController.handleRequest(AbstractController.java:153)
    at org.labkey.api.action.SpringActionController.handleRequest(SpringActionController.java:336)
    at org.labkey.api.module.DefaultModule.dispatch(DefaultModule.java:726)
    at org.labkey.api.view.ViewServlet.service(ViewServlet.java:140)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
    at org.labkey.api.data.TransactionFilter.doFilter(TransactionFilter.java:36)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:215)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
    at org.labkey.core.filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:124)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:215)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
    at org.labkey.api.module.ModuleLoader.doFilter(ModuleLoader.java:651)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:215)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
    at org.labkey.api.security.AuthFilter.doFilter(AuthFilter.java:101)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:215)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:172)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
    at org.apache.catalina.valves.FastCommonAccessLogValve.invoke(FastCommonAccessLogValve.java:482)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:875)
    at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665)
    at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528)
    at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81)
    at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:689)
    at java.lang.Thread.run(Thread.java:637)