That is the correct answer, here is the longer version.
Sometimes it feels easier to hack a method to work both ways, but it is Bad(tm). You probably aren't using and data in self if you can call it with & without an instance. This means you should be doing

$answer = Package::foo($ob->member)
or
$answer = Package::foo('hibill')
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If you are doing using something in $self if it is an object, and doing something slightly different if it is being called as a package function, then it isn't the same function. In this case put the common functionality in foo_common() and have two subs - one for instaces and one for class method - that do the slightly different things. This will make the code readable because people can tell they are different without having to know that soemthing in $self is used invisibly.

-jackdied