In the case provided by a customer it was with JIRA-delegation user management. However, we should be more liberal in what this code handles. It shouldn't die if the user doesn't exist.

Sample stack trace:

java.lang.NullPointerException
at com.atlassian.confluence.rss.DefaultFeedBuilder.getUserFullName(DefaultFeedBuilder.java:171)
at com.atlassian.confluence.rss.DefaultFeedBuilder.createFeed(DefaultFeedBuilder.java:69)
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:585)
at org.springframework.aop.framework.AopProxyUtils.invokeJoinpointUsingReflection(AopProxyUtils.java:61)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:149)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:116)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:56)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:138)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:152)
at $Proxy25.createFeed(Unknown Source)
at com.atlassian.confluence.spaces.actions.CreateRssFeedAction.getSyndFeed(CreateRssFeedAction.java:42)