title: disable/ enable primefaces components
body: <p>I want to disable some primefaces components after a selection from <code>p:selectOneMenu</code> but when I choose no selection option it still disabled</p>
  
  <pre><code>&lt;p:outputLabel value="Manager" style="color:white;font-weight: bold;" /&gt;
  &lt;p:selectOneMenu id="manager" value="#{employeeMB.selectedManager}" immediate="true"&gt;
       &lt;f:selectItem itemLabel="Selectionner..." noSelectionOption="true"/&gt;
       &lt;f:selectItems value="#{employeeMB.managers}"  /&gt;
       &lt;p:ajax update="managerSelect role"  /&gt;
  &lt;/p:selectOneMenu&gt;
  
  &lt;p:outputLabel value="Est un Manager" 
                 style="color:white;font-weight: bold;" /&gt;
  &lt;p:selectBooleanCheckbox id="managerSelect" 
                           value="#{employeeMB.employee.isManager}" 
                           disabled="#{employeeMB.selectedManager != null}" /&gt;
  
  &lt;p:outputLabel for="role" value="Role Utilisateur" style="color:white;font-weight: bold;" /&gt;
  &lt;p:selectManyCheckbox id="role" value="#{employeeMB.selectedRoles}"&gt;
      &lt;f:selectItem itemLabel="Employée" itemValue="ROLE_EMPLOYEE" /&gt;
      &lt;f:selectItem itemLabel="Manager" itemValue="ROLE_MANAGER" itemDisabled="#{employeeMB.selectedManager != null}"/&gt;
      &lt;f:selectItem itemLabel="RH" itemValue="ROLE_RH" itemDisabled="#{employeeMB.selectedManager != null}"/&gt;
  &lt;/p:selectManyCheckbox&gt;
  </code></pre>