p:datatable multiple select with checkboxes. Rowtoggler triggers event - jsf

Question

I have a datatable inside another datatable. The nested table I need to have a multiple selection checkboxes, a button to fire actionlistener and a p:rowToggler to show more data in row. The toggler and commandbutton works fine without the selection column in the table, but when I add this column the commandButton doesn't go to the backing bean, toggler on click doesn't work properly, and setSelected isn't called. Both throw a NP. I'm using 3.4.2 is this feature on newer releases only?
SEVERE: FullAjaxExceptionHandler: An exception occurred during processing JSF ajax request. Error page '/error.xhtml' will be shown.
java.lang.NullPointerException
Table
<p:dataTable id="gro" var="g" value="#{requestBean.main.childRequest}" styleClass="veaGrid"
paginator="true" rows="1" paginatorTemplate="{CurrentPageReport}" >
<p:column>
<p:ajaxStatus >
<f:facet name="start">
<p:graphicImage value="/resources/images/ajaxloadingbar.gif" />
</f:facet>
<f:facet name="complete">
<h:outputText value="" />
</f:facet>
</p:ajaxStatus>
<p:dataTable id="group" var="g2" value="#{g.groups}" rowKey="#{g2.group_name}" selection="#{requestBean.selectedGroups}" >
<p:column selectionMode="multiple" style="width:2%" />
<p:column headerText="#{g.systemCd} - Groups" style="width:25%" >
#{g2.group_name}
</p:column>
<p:column style="width:2%">
View Users <p:rowToggler />
</p:column>
<p:rowExpansion>
<p:dataTable styleClass="veaGrid" var="g3" value="#{g2.group_members}" sortOrder="descending"
paginator="true" rows="10"
paginatorTemplate="{CurrentPageReport} {FirstPageLink} {PreviousPageLink} {PageLinks} {NextPageLink} {LastPageLink} {RowsPerPageDropdown}"
filteredValue="#{requestBean.filteredMembers}">
<p:column filterBy="#{g3.first_name}">
<h:outputText value="#{g3.first_name}"/>
</p:column>
<p:column filterBy="#{g3.last_name}">
<h:outputText value="#{g3.last_name}"/>
</p:column>
<p:column filterBy="#{g3.signon}">
<h:outputText value="#{g3.signon}"/>
</p:column>
</p:dataTable>
</p:rowExpansion>
</p:dataTable>
<center>
<p:commandButton id="continue" value="Continue" actionListener="#{requestBean.saveGroups}"/>
</center>
</p:column>
</p:dataTable>

Answer 1

Found the problem.. I had the requestBean.selectedGroups set to
ArrayList<Group>
I changed the property to
Group[]
and now everything is functional again.