GB Classic 12.x: Error when clicking on assignment name

Caused by: org.apache.jasper.JasperException: An exception occurred processing JSP page [/assignmentDetails.jsp] at line [12]

9:      <h:form id="gbForm" onsubmit="return blockDoubleSubmit();">
10:
11:
12:             <sakai:flowState bean="#{assignmentDetailsBean}" />
13:
14:             <t:aliasBean alias="#{bean}" value="#{assignmentDetailsBean}">
15:                     <%@ include file="/inc/appMenu.jspf"%>


Stacktrace:
        at org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:584)
        at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:481)
        at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:386)
        at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:330)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
        at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
        at org.apache.myfaces.webapp.filter.ExtensionsFilter.doFilter(ExtensionsFilter.java:311)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
        at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:728)
        at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:470)
        at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:395)
        at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:316)
        at org.apache.myfaces.context.servlet.ServletExternalContextImpl.dispatch(ServletExternalContextImpl.java:419)
        ... 69 more
Caused by: java.lang.NullPointerException
        at java.util.Collections.sort(Collections.java:141)
        at org.sakaiproject.tool.gradebook.ui.AssignmentDetailsBean$ScoreRow.<init>(AssignmentDetailsBean.java:90)
        at org.sakaiproject.tool.gradebook.ui.AssignmentDetailsBean.init(AssignmentDetailsBean.java:454)
        at org.sakaiproject.tool.gradebook.ui.InitializableBean.startRenderResponse(InitializableBean.java:62)
        at org.sakaiproject.jsf.component.FlowState.encodeBegin(FlowState.java:119)
        at javax.faces.webapp.UIComponentTag.encodeBegin(UIComponentTag.java:467)
        at javax.faces.webapp.UIComponentTag.doStartTag(UIComponentTag.java:320)
        at org.apache.jsp.assignmentDetails_jsp._jspx_meth_sakai_005fflowState_005f0(assignmentDetails_jsp.java:776)
        at org.apache.jsp.assignmentDetails_jsp._jspService(assignmentDetails_jsp.java:453)
        at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
        at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:443)
        ... 85 more