WHICH undefined is not a function?

var maybeFunction = function(i) { if (i === 6) { return; } return function() {}; }; var i = 0; maybeFunction(i++)(); maybeFunction(i++)(); maybeFunction(i++)(); maybeFunction(i++)(); maybeFunction(i++)(); maybeFunction(i++)(); maybeFunction(i++)(); maybeFunction(i++)(); maybeFunction(i++)(); maybeFunction(i++)(); // see you when you get done counting by hand!