title: el expression: empty a or a.method(b) throw npe of a.method(b)
body: <pre><code>&lt;h:outputText styleClass="fa fa-android" rendered="#{empty module.platform or module.platform.includePlatforms(Platform.PLATFORM_ANDROID)}"/&gt;
  </code></pre>
  
  <p>The expressions above throws the flowing exception:</p>
  
  <pre><code>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]
      ...
  </code></pre>
  
  <p><code>empty module.platform</code> has tested nullability of module.platform. So I think that if <code>module.platform</code> is null, <code>module.platform.includePlatforms(Platform.PLATFORM_ANDROID)</code> will not be invoked. Then why npe is throwed by myfaces?
  My myfaces version is 2.2.9.</p>
  
  <p>I found the problem is not el expression. <code>module.platform</code> is not null. <code>Platform.PLATFORM_ANDROID</code> is null. However, it is not always null. it is sometimes null.</p>
  
  <pre><code>&lt;p:importConstants type="com.bolan.fzsystem.core.model.Platform" var="Platform" /&gt;
  </code></pre>
  
  <p>I import Platform.PLATFORM_ANDROID by <code>p:importConstants</code>.</p>