Field Validate in Spring Web Flow

I am trying to do my field validate inside the controller of my Spring Web Flow. I have the following code inside my code and it works great if I have a error but if I dont have a error what do I return? Am I doing this the right why?

Code in my controller:
public Event validateVisit(Visit visit, MessageContext messageContext)
{
String temp = visit.getType_of_visit() + "";
if(temp.equals(""))
{
MessageBuilder errorMessageBuilder = new MessageBuilder().error();
errorMessageBuilder.source("type_of_visit");
errorMessageBuilder.code("type_of_visit_missing");
messageContext.addMessage(errorMessageBuilder.buil d());
return new EventFactorySupport().error(this);
}
}

Here is my flow.xml
<view-state id="SchoolVisitReport" view="SchoolVisitReport.jsp" model="visit">
<transition on="submit" to="addVisit">
<evaluate expression="flowActions.validateVisit(visit, messageContext)"/>
</transition>
<transition on="cancel" to="endState"/>
</view-state>

<decision-state id="addVisit">
<if test="flowActions.addVisit(visit)" then="endState" else="errorState" />
</decision-state>

Please let me know if I am doing this the right what.. I cant get it working if I dont have a error.