jsf - 它提供 PropertyNotFoundException Primefaces pieModel 和 JSFBeans

Question

 <f:event type="preRenderView"
                listener="#{fewosByRegionBean.getFewosByRegion().pieModel}"/>
        </f:metadata>
<p:chart id="pie" type="pie" model="#{fewosByRegionBean.getFewosByRegion().pieModel}" responsive="true" />

它提供了 PropertyNotfoundexception，但我不明白为什么，因为我有 getter 和 setter

javax.el.PropertyNotFoundException: /pages/protected/search2.xhtml @23,67 listener="#{fewosByRegionBean.getFewosByRegion().pieModel}": Target Unreachable, 'null' returned null