Why is parameter sometimes null by JSF Parameter passing?

Question

I pass the managedbean that i use (myBean) as parameter to another managedbean(PersonRoleSearch) so that I can call the methods of the first bean (myBean). But sometimes the parameter is null, therefore i get nullpointer exception. There is no explanation for me why it occurs.

<a4j:commandLink id="PersonSearch" styleClass="no-decor"
                        status="noAjaxStatus" execute="@searchGemOrderGroup"
                        immediate="true"
                        oncomplete="#{rich:component('personRoleSearchPopupPanel')}.show()"
                        action="#{personRoleSearch.doInit(myBean)}"
                        render="personRoleSearchPopupPanel">
                        <h:graphicImage value="/resources/icons/blue/searchperson.png"
                            alt="#{msg['personSearch.search']}" />
                    </a4j:commandLink>

Hier ist the init method of Personrolesearch

 public void doInit(final MyBean target){...}

 public void doSomething(){
   target.myBeanMethod();

    ...}

What can be the reason?