SelectOneMenu required when a certain button is pressed

Question

I have a required select one menu but the required message appeares also in Back button. I want it to be active only when the Create button pressed. No validation needed for Back button. How can i do that?

 <h:selectOneMenu id="typeKey" value="#{bean.Type}"
   required="#{not empty xx}"
   requiredMessage="SELECTION REQUIRED">
 ...