Compare two strings in freemarker

I have used the following syntax to compare two string values in freemarker.

<#if parameters.isvalid == "true">

//if isvalid is a string variable...
<#if parameters?? && parameters.isvalid?? && parameters.isvalid="true">
     blah blah
<#else>
     lah lah
</#if>

//if isvalid is a boolean variable...
<#if parameters?? && parameters.isvalid?? && parameters.isvalid=true>
     blah blah
<#else>
     lah lah
</#if>

See the deails