Missing group causes portlets to break with stacktrace

After upgrading to 3.13, a few JIRA instances of ours broke, either when creating issues, or on a portlet. The stacktrace is:

We were unable to render this portlet due to an internal error. Please contact your JIRA Administrator.
Exception thrown while rendering portlet of type 'Admin' with id of '10006' on dashboard with id '10000'
java.lang.NullPointerException at com.atlassian.jira.user.util.UserUtilImpl.getActiveUserCount(UserUtilImpl.java:138) at com.atlassian.jira.user.util.UserUtilImpl.canActivateNumberOfUsers(UserUtilImpl.java:185) at com.atlassian.jira.portal.portlets.AdminPortlet.getVelocityParams(AdminPortlet.java:59) at com.atlassian.jira.portal.PortletImpl.getViewHtml(PortletImpl.java:117) at com.atlassian.jira.web.portlet.bean.PortletRenderer.getNormalHtml(PortletRenderer.java:80) at com.atlassian.jira.web.portlet.bean.PortletRenderer.renderPortlet(PortletRenderer.java:60) at com.atlassian.jira.web.component.DashboardPageWebComponent.renderPortlet(DashboardPageWebComponent.java:207) at sun.reflect.GeneratedMethodAccessor51.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:585) at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.invoke(UberspectImpl.java:267) at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:197) at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:175) at org.apache.velocity.runtime.parser.node.ASTReference.render(ASTReference.java:220) at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:55) at org.apache.velocity.runtime.parser.node.ASTIfStatement.render(ASTIfStatement.java:70) at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:55) at org.apache.velocity.runtime.directive.Foreach.render(Foreach.java:166) at org.apache.velocity.runtime.parser.node.ASTDirective.render(ASTDirective.java:114) at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:55) at org.apache.velocity.runtime.directive.Foreach.render(Foreach.java:166) at org.apache.velocity.runtime.parser.node.ASTDirective.render(ASTDirective.java:114) at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:55) at org.apache.velocity.runtime.parser.node.ASTIfStatement.render(ASTIfStatement.java:70) at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:230) at org.apache.velocity.Template.merge(Template.java:256) at org.apache.velocity.app.VelocityEngine.mergeTemplate(VelocityEngine.java:450) at com.atlassian.velocity.DefaultVelocityManager.getEncodedBody(DefaultVelocityManager.java:77) at com.atlassian.velocity.DefaultVelocityManager.getEncodedBody(DefaultVelocityManager.java:61) at com.atlassian.velocity.DefaultVelocityManager.getEncodedBody(DefaultVelocityManager.java:56) at com.atlassian.jira.web.component.AbstractWebComponent.getHtml(AbstractWebComponent.java:33) at com.atlassian.jira.web.component.DashboardPageWebComponent.getHtml(DashboardPageWebComponent.java:177) at org.apache.jsp.secure.views.dashboard_jsp._jspService(dashboard_jsp.java:190) at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98) at javax.servlet.http.HttpServlet.service(HttpServlet.java:803) at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:328) at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:315) at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265) at javax.servlet.http.HttpServlet.service(HttpServlet.java:803) at
...

We tracked the cause down to the JIRA "Use" global permission being granted to a non-existent group.

Previous versions of JIRA ignored non-existent groups, but 3.13 blows up.