How to tell if the requested node exists?

Im trying to add a function to my common.init that is basically

<#if node exists > do stuff </#if>

I tried the following but no luck.

<#if !coreNode>

<#if !coreNode.id>

<#if !coreNode.ancestors>

<#if page.name == "ErrorPage">

but none of them actually run their contents on a nonexistant node. Is there a way to check if the requested node exists?