SEC-719: removed explicit toString() call to prevent NPE when userInfo is null

portlet/src/main/java/org/springframework/security/ui/portlet/PortletAuthenticationDetails.java

@@ -28,6 +28,6 @@ public class PortletAuthenticationDetails implements Serializable {
     }
     
     public String toString() {
-    	return "User info: " + userInfo.toString();
+    	return "User info: " + userInfo;
     }
 }