Unable to load Favorite Filter if filter shared with user who doesn't have unique key mapping

[c.a.j.rest.exception.ExceptionInterceptor] Returning internal server error in response
java.lang.reflect.InvocationTargetException
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at com.atlassian.plugins.rest.common.interceptor.impl.DispatchProviderHelper$ResponseOutInvoker$1.invoke(DispatchProviderHelper.java:192)
        ... 4 filtered
        at com.atlassian.jira.rest.exception.ExceptionInterceptor.intercept(ExceptionInterceptor.java:55)
        ... 1 filtered
        at com.atlassian.jira.rest.v2.issue.scope.RequestScopeInterceptor.intercept(RequestScopeInterceptor.java:39)
        ... 15 filtered
        at com.atlassian.plugins.rest.module.RestDelegatingServletFilter$JerseyOsgiServletContainer.doFilter(RestDelegatingServletFilter.java:154)
        ... 1 filtered
        at com.atlassian.plugins.rest.module.RestDelegatingServletFilter.doFilter(RestDelegatingServletFilter.java:68)
        ... 36 filtered
        at com.atlassian.web.servlet.plugin.request.RedirectInterceptingFilter.doFilter(RedirectInterceptingFilter.java:21)
        ... 53 filtered
        at com.atlassian.jira.security.JiraSecurityFilter.lambda$doFilter$0(JiraSecurityFilter.java:76)
        ... 1 filtered
        at com.atlassian.jira.security.JiraSecurityFilter.doFilter(JiraSecurityFilter.java:74)
        ... 16 filtered
        at com.atlassian.plugins.rest.module.servlet.RestSeraphFilter.doFilter(RestSeraphFilter.java:37)
        ... 20 filtered
        at com.atlassian.jira.servermetrics.CorrelationIdPopulatorFilter.doFilter(CorrelationIdPopulatorFilter.java:30)
        ... 10 filtered
        at com.atlassian.web.servlet.plugin.request.RedirectInterceptingFilter.doFilter(RedirectInterceptingFilter.java:21)
        ... 4 filtered
        at com.atlassian.web.servlet.plugin.LocationCleanerFilter.doFilter(LocationCleanerFilter.java:36)
        ... 29 filtered
        at com.atlassian.jira.servermetrics.MetricsCollectorFilter.doFilter(MetricsCollectorFilter.java:25)
        ... 27 filtered
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Thread.java:748)
Caused by: com.atlassian.util.concurrent.LazyReference$InitializationException: java.lang.IllegalStateException: User 'testuser' has no unique key mapping.
        at com.atlassian.util.concurrent.LazyReference.getInterruptibly(LazyReference.java:149)
        at com.atlassian.util.concurrent.LazyReference.get(LazyReference.java:112)
        at com.atlassian.jira.rest.v2.search.UserListResolver.getShareUsers(UserListResolver.java:114)
        at com.atlassian.jira.rest.v2.search.UserListResolver.getShareCount(UserListResolver.java:128)
        at com.atlassian.jira.rest.v2.search.UserBeanListWrapper.<init>(UserBeanListWrapper.java:31)
        at com.atlassian.jira.rest.v2.search.FilterResource$SearchRequestToFilterBean.apply(FilterResource.java:682)
        at com.atlassian.jira.rest.v2.search.FilterResource.getFilter(FilterResource.java:159)
        ... 238 more
Caused by: java.lang.IllegalStateException: User 'testuser' has no unique key mapping.
 at com.atlassian.jira.user.ApplicationUsers.from(ApplicationUsers.java:46)
        at com.atlassian.jira.user.ApplicationUsers.from(ApplicationUsers.java:120)
        at com.atlassian.jira.security.groups.DefaultGroupManager.getUsersInGroup(DefaultGroupManager.java:163)
        at com.atlassian.jira.security.groups.DefaultGroupManager.getUsersInGroup(DefaultGroupManager.java:192)
        at com.atlassian.jira.security.groups.RequestCachingGroupManager.getUsersInGroup(RequestCachingGroupManager.java:133)
        ... 2 filtered

UPDATE app_user SET lower_user_name = user_key WHERE user_key = 'testuser';