Riamus2 was talking about your typo. You said "if ($1 == $null)" when you meant "if ($1 != $null)".
Well, in case you didn't mean the latter, you're wrong - after all, ($1 == $null) and ($1) are the same (equally false) when $1 is 0 or $false.
And you're wrong about "if ($1)" being true when $1 is "$false": $false returns itself (as does $true). The mIRC interpreter checks its result, just like with any other identifier, but the result in this case is "$false" itself. So, it doesn't matter if you're providing the literal text or the identifier in the statement, because mIRC will treat them equally.
Try: //tokenize 32 $!false | if (!$1) echo -a even the literal "$false" is false
