template condition that checks if a field is blank

[RedTyger]

<if condition="is_member_of($post, 17) OR is_member_of($post, 18) OR is_member_of($post, 6)">
<if condition="$userinfo[field1] == ''">
<a class="smallfont" target="_blank" href="http://url.com?address=$userinfo[field1]">Linky</a>
<else />
<a class="smallfont" target="_blank" href="http://url.com?address=$post[musername]">Linky</a>
</if>
</if>