Good script.

here:

on *:text:!ustats*:#: {
if (%lines- [ $+ [ $2 ] ] != $null) {
    msg $chan $nick $+ : $2 Has Writen %lines- [ $+ [ $2 ] ] lines.
}
else {
    msg $chan $2 Has Writen 0 Lines
}
}

Could be:

on *:text:!ustats*:#: {
    msg $chan $nick $+ : $2 Has Writen $iif(!%lines- [ $+ [ $2 ] ],0,%lines- [ $+ [ $2
] ]) line(s).
}

That would return 0 if the variable is $null :)