Description of problem:
Attempt to add notification for the second alert definition in JBoss ON UI throws message "Failed to get notification configuration preview".


Version-Release number of selected component (if applicable):
JBoss ON 3.3.7

How reproducible:
Always

Steps to Reproduce:
1. Navigate to JBoss ON UI -> Inventory -> Servers -> RHQ Agent -> Alert -> Definition;
2. Click on "New" button;
3. In "General Properties", Enter Alert name;
4. Navigate to Conditions, Add a condition like, "Condition Type: Measurement Absolute Value Threshold, Metric: Agent server Clock Different", Fill some values for other boxes;
5. Navigate to "Notifications", Click Add, "Notification Sender: System User", select assigned user as "rhqadmin", Click OK;
6. Click on "Save";
7. Click on "Back to List";
8. Repeat from Step #2 again


Actual results:
Attempt to configure notification for the second alert definition logs message "Failed to get notification configuration preview" and "Configuration" column in the Notification tab shows "unknown". If "Save" button is pressed, above message is deleted and "Configuration" column will be set to "rhqadmin".


Expected results:
No error message is thrown;

Additional info:

At the time when "Failed to get notification configuration preview" message is shown, server.log file logs the following:

***********************************************************************
ERROR [org.apache.catalina.core.ContainerBase.[jboss.web].[default-host].[/coregui]] (http-10.33.24.113:7080-1) org.rhq.coregui.CoreGUI AlertDefinitionGWTService: An IncompatibleRemoteServiceException was thrown while processing this call.: com.google.gwt.user.client.rpc.IncompatibleRemoteServiceException: Attempt to deserialize an object of type class org.rhq.core.domain.alert.AlertCondition when an object of type class org.rhq.core.domain.alert.AlertDefinition is expected
        ...
	at org.rhq.helpers.rtfilter.filter.RtFilter.doFilter(RtFilter.java:125) [rhq-rtfilter-4.12.0.JON330GA-redhat-1.jar:4.12.0.JON330GA-redhat-1]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:246) [jbossweb-7.5.16.Final-redhat-1.jar:7.5.16.Final-redhat-1]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:214) [jbossweb-7.5.16.Final-redhat-1.jar:7.5.16.Final-redhat-1]
	at org.rhq.coregui.server.filter.CacheControlFilter.doFilter(CacheControlFilter.java:71) [classes:]
        ...
Caused by: com.google.gwt.user.client.rpc.SerializedTypeViolationException: Attempt to deserialize an object of type class org.rhq.core.domain.alert.AlertCondition when an object of type class org.rhq.core.domain.alert.AlertDefinition is expected
	at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamReader.deserialize(ServerSerializationStreamReader.java:636) [gwt-servlet-2.5.0.jar:]
	at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamReader.readObject(ServerSerializationStreamReader.java:567) [gwt-servlet-2.5.0.jar:]
	at com.google.gwt.user.server.rpc.core.java.util.Collection_ServerCustomFieldSerializerBase.deserialize(Collection_ServerCustomFieldSerializerBase.java:38) [gwt-servlet-2.5.0.jar:]
        ...
***********************************************************************