el expression: empty a or a.method(b) throw npe of a.method(b)

Question

<h:outputText styleClass="fa fa-android" rendered="#{empty module.platform or module.platform.includePlatforms(Platform.PLATFORM_ANDROID)}"/>

The expressions above throws the flowing exception:

org.apache.myfaces.view.facelets.el.ContextAwareELException: javax.el.ELException: java.lang.NullPointerException
    at org.apache.myfaces.view.facelets.el.ContextAwareTagValueExpression.getValue(ContextAwareTagValueExpression.java:104) ~[myfaces-impl-2.2.9.jar!/:2.2.9]
    ...
Caused by: java.lang.NullPointerException
    at com.bolan.fzsystem.core.model.Platform.includePlatforms(Platform.java:61) ~[fzSystem-model-5.0.jar:?]
    at sun.reflect.GeneratedMethodAccessor543.invoke(Unknown Source) ~[?:?]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_45]
    at java.lang.reflect.Method.invoke(Method.java:497) ~[?:1.8.0_45]
    at javax.el.ELUtil.invokeMethod(ELUtil.java:308) ~[jboss-el-api_3.0_spec-1.0.4.Final.jar!/:1.0.4.Final]
    at javax.el.BeanELResolver.invoke(BeanELResolver.java:537) ~[jboss-el-api_3.0_spec-1.0.4.Final.jar!/:1.0.4.Final]
    at javax.el.CompositeELResolver.invoke(CompositeELResolver.java:256) ~[jboss-el-api_3.0_spec-1.0.4.Final.jar!/:1.0.4.Final]
    ...

empty module.platform has tested nullability of module.platform. So I think that if module.platform is null, module.platform.includePlatforms(Platform.PLATFORM_ANDROID) will not be invoked. Then why npe is throwed by myfaces? My myfaces version is 2.2.9.

I found the problem is not el expression. module.platform is not null. Platform.PLATFORM_ANDROID is null. However, it is not always null. it is sometimes null.

<p:importConstants type="com.bolan.fzsystem.core.model.Platform" var="Platform" />

I import Platform.PLATFORM_ANDROID by p:importConstants.