As a GreenHopper admin I can't configure task board mappings (NullPointerException)

I upgraded to JIRA 3.13.2 and GreenHopper 3.2.1-jira313. Now I can't configure the task board mappings since when I try to press the "Update" button I get NullPointerException (HTTP 500) response with the following stacktrace:
java.lang.NullPointerException
Stack Trace: java.lang.NullPointerException
at com.pyxis.greenhopper.jira.actions.ConfigurationAction.getDuplicatas(ConfigurationAction.java:308)
at com.pyxis.greenhopper.jira.actions.ConfigurationAction.doSetStepDefinition(ConfigurationAction.java:120)
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:597)
at webwork.util.InjectionUtils$DefaultInjectionImpl.invoke(InjectionUtils.java:61)
at webwork.util.InjectionUtils.invoke(InjectionUtils.java:52)
at webwork.action.ActionSupport.invokeCommand(ActionSupport.java:417)
at webwork.action.ActionSupport.execute(ActionSupport.java:146)
at com.atlassian.jira.action.JiraActionSupport.execute(JiraActionSupport.java:54)
at webwork.dispatcher.GenericDispatcher.executeAction(GenericDispatcher.java:132)
...

Referer URL:
http://jira:8080/secure/Configuration.jspa?decorator=none&selectedProjectId=10000&taskBoard=true