===== <#NullStr> =====

This tag return the "null" string (Ascii char #2). The null string is use in some case 
to differentiate empty string ('') from not assigned string

==== Example ====

<code>
<#if condition="('<#Analytics_Trackers[<#i>].pages[<#j>].ReferrerOverride>' <> '<nullstr>')">....<#endif>
</code>