gistfile1.txt

# When anything, including nil, is a valid param and you need
# a clear way to know if a param was set or not, use `None`.

None = Object.new

def foo(a, b=None)
  result = [a]
  if b != None
    result << b
  end
  result
end

That feels like something _why would do.

Which is to say, awesome.

;)

See also: https://gist.github.com/760597