Description of problem:
While adding platform to group, null pointer exception is thrown.

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


How reproducible:
100%

Steps to Reproduce:
1. Click on Groups and then click on new group.
2. Enter the Group name and select mixed group and click ok.
3. Now, click on add to group and from filter dropdown, select platform.
  
Actual results:
We get java null pointer exception.

Expected results:
It should list the platforms.

Additional info:
The group works well for server and service type filter. However, for platform it fails. 

java.lang.NullPointerException at org.rhq.enterprise.gui.legacy.action.resource.group.inventory.AddGroupResourcesFormPrepareAction.buildResourceList(AddGroupResourcesFormPrepareAction.java:204) at org.rhq.enterprise.gui.legacy.action.resource.group.inventory.AddGroupResourcesFormPrepareAction.execute(AddGroupResourcesFormPrepareAction.java:158) at org.rhq.enterprise.gui.legacy.action.BaseRequestProcessor.processActionPerform(BaseRequestProcessor.java:46) at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236) at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196) at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414) at javax.servlet.http.HttpServlet.service(HttpServlet.java:690) at javax.servlet.http.HttpServlet.service(HttpServlet.java:803) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:654) at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:557) at