primefaces datatable row returns null value after filtering - jsf

Question

I have a primefaces datatable which displays a list of cars. One of the columns of the datatable has a command button which when clicked opens a dialog box which displays information about the selected car. Everything works as expected until I default filter the datatable and select the command button of a filtered row. The details of the car is null in this case. How can I get the value (car object) of the selected row after filtering?
<h:form id="carView">
<h:panelGrid id="carPanelGroup" style="width:100%" styleClass="tblNowrap100pct">
`<p:dataTable value="#{carBean.carList}" var="car" id="carTbl" stripedRows="true" rendered="#{not empty carBean.carList}" showGridlines="true" styleClass="tblNowrap100pct" filteredValue="#{carBean.filteredValues}" rowKey="#{car.carId}">
<p:column headerText="Car Name" sortBy="#{car.carName}" filterBy="#{car.carName}" filterMatchMode="contains" >
<f:facet name="header">
<h:outputText value="Car Name" />
</f:facet>
<h:outputText value="#{car.carName}" />
</p:column>
<p:column headerText="Make" sortBy="#{car.make}" filterBy="#{car.make}" filterMatchMode="contains">
<f:facet name="header">
<h:outputText value="Make" />
</f:facet>
<h:outputText value="#{car.make}" />
</p:column>
<p:column>
<f:facet name="header">
<h:outputText value="Car Download" />
</f:facet>
<p:commandButton action="#{carBean.selectCar}" value="Download" styleClass="linkButton" process="#this" oncomplete="PF('carDownloadpanel').show();" update="#all">
<f:setPropertyActionListener value="#{car}" target="#{carBean.carDto}"/>
</p:commandButton>
</p:column>`
</p:dataTable>
</p:panelGrid>
</h:form>
<!-- ******** pop up -->
<p:outputPanel id = "downloadOutputPanel">
<p:dialog header="#{carBean.carDto.carName}" widgetVar="carDownloadpanel" width="500" height="400" id="dialogDetails" modal="true">
<f:facet name="header">
<h:panelGroup>
<h:outputText value="#{carBean.carDto.carName}" />
</h:panelGroup>
</f:facet>
<h:form id="carDetailView">
<p:panel>
<p:panelGrid id="carDetails" columns="2" styleClass="summaryTable"
columnClasses="colLabel, colNormalInputArea" rendered="#{not empty firmBean.firmDto}">
<h:outputText value="Car Name:" />
<h:outputText value="#{carBean.carDto.carName}" />
<h:outputText value="Firm Id:" />
<h:outputText value="#{carBean.carDto.carId}" />
</p:panelGrid>
</p:panel>
</h:form>
<h:form id="iwaInfo">
<h:panelGrid id="carReportInput" columns="2" styleClass="summaryTable" columnClasses="colLabel, colNormalInputArea">
<p:commandLink value="Download" id="downloadBtn"
action="#{carBean.downloadCar}" onclick="PF('carDownloadpanel').hide();">
</p:commandLink>
<p:commandLink value="Cancel" id="cancelBtn"
oncomplete="PF('carDownloadpanel').hide();" update=":carView:carPanelGroup" process="#parent"/>
</h:panelGrid>
</h:form>
</p:dialog>
</p:outputPanel>
Java method :
public String selectCar(){
if (this.carDto != null) {
carId = this.carDto.getCarId();
instanceId = this.carDto.getInstanceId();
if (carId!=null&&instanceId!=null){
CarDto dto = new CarDto();
List<CarDto> sLst = carService.searchCar(Long.parseLong(carId), Long.parseLong(instanceId));
if (sLst!=null&&sLst.size()>0){
dto= sLst.get(0);
}
setCarDto(dto);
}
}
return "";
}