LDAP to Keycloak attribute mapping cannot handle arrays

Create a new LDAP user. Add an attribute more than once. eg applications=keycloak and applications=website. Create a federation attribute mapper to map this attribute into Keycloak. On federation sync you get the following error trace which indicates that a tree (multi-attribute) cannot be cast to a string. 2015-06-19 15:14:30,878 INFO [org.keycloak.federation.ldap.LDAPFederationProviderFactory] (default task-6) Sync all users from LDAP to local store: realm: master, federation provider: PI ordinary users 2015-06-19 15:14:31,124 ERROR [io.undertow.request] (default task-6) UT005023: Exception handling request to /auth/admin/realms/master/user-federation/instances/141db483-1f5c-412f-acbb-0ea642015798/sync: java.lang.RuntimeException: request path: /auth/admin/realms/master/user-federation/instances/141db483-1f5c-412f-acbb-0ea642015798/sync at org.keycloak.services.filters.KeycloakSessionServletFilter.doFilter(KeycloakSessionServletFilter.java:54) at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:60) at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:132) at io.undertow.servlet.handlers.FilterHandler.handleRequest(FilterHandler.java:85) at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62) at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36) at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78) at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:131) at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57) at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46) at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64) at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:58) at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:72) at io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50) at io.undertow.security.handlers.SecurityInitialHandler.handleRequest(SecurityInitialHandler.java:76) at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61) at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:274) at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:253) at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:80) at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:172) at io.undertow.server.Connectors.executeRootHandler(Connectors.java:199) at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:774) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745) Caused by: org.jboss.resteasy.spi.UnhandledException: java.lang.ClassCastException: java.util.TreeSet cannot be cast to java.lang.String at org.jboss.resteasy.core.ExceptionHandler.handleApplicationException(ExceptionHandler.java:76) at org.jboss.resteasy.core.ExceptionHandler.handleException(ExceptionHandler.java:212) at org.jboss.resteasy.core.SynchronousDispatcher.writeException(SynchronousDispatcher.java:149) at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:372) at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:179) at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:220) at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:56) at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:51) at javax.servlet.http.HttpServlet.service(HttpServlet.java:790) at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:86) at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:130) at org.keycloak.services.filters.ClientConnectionFilter.doFilter(ClientConnectionFilter.java:41) at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:60) at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:132) at org.keycloak.services.filters.KeycloakSessionServletFilter.doFilter(KeycloakSessionServletFilter.java:40) ... 29 more Caused by: java.lang.ClassCastException: java.util.TreeSet cannot be cast to java.lang.String at org.keycloak.federation.ldap.mappers.UserAttributeLDAPFederationMapper.onImportUserFromLDAP(UserAttributeLDAPFederationMapper.java:60) at org.keycloak.federation.ldap.LDAPFederationProvider.importLDAPUsers(LDAPFederationProvider.java:404) at org.keycloak.federation.ldap.LDAPFederationProviderFactory.importLdapUsers(LDAPFederationProviderFactory.java:269) at org.keycloak.federation.ldap.LDAPFederationProviderFactory$1.run(LDAPFederationProviderFactory.java:223) at org.keycloak.models.utils.KeycloakModelUtils.runJobInTransaction(KeycloakModelUtils.java:241) at org.keycloak.federation.ldap.LDAPFederationProviderFactory.syncImpl(LDAPFederationProviderFactory.java:219) at org.keycloak.federation.ldap.LDAPFederationProviderFactory.syncAllUsers(LDAPFederationProviderFactory.java:177) at org.keycloak.services.managers.UsersSyncManager.syncAllUsers(UsersSyncManager.java:50) at org.keycloak.services.resources.admin.UserFederationProviderResource.syncUsers(UserFederationProviderResource.java:144) 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:497) at org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:137) at org.jboss.resteasy.core.ResourceMethodInvoker.invokeOnTarget(ResourceMethodInvoker.java:296) at org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:250) at org.jboss.resteasy.core.ResourceLocatorInvoker.invokeOnTargetObject(ResourceLocatorInvoker.java:140) at org.jboss.resteasy.core.ResourceLocatorInvoker.invoke(ResourceLocatorInvoker.java:109) at org.jboss.resteasy.core.ResourceLocatorInvoker.invokeOnTargetObject(ResourceLocatorInvoker.java:135) at org.jboss.resteasy.core.ResourceLocatorInvoker.invoke(ResourceLocatorInvoker.java:109) at org.jboss.resteasy.core.ResourceLocatorInvoker.invokeOnTargetObject(ResourceLocatorInvoker.java:135) at org.jboss.resteasy.core.ResourceLocatorInvoker.invoke(ResourceLocatorInvoker.java:109) at org.jboss.resteasy.core.ResourceLocatorInvoker.invokeOnTargetObject(ResourceLocatorInvoker.java:135) at org.jboss.resteasy.core.ResourceLocatorInvoker.invoke(ResourceLocatorInvoker.java:103) at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:356) ... 40 more