Instantiating a class with an undefined amount fails without a helpful message

[Roland van Ipenburg]

Throw an exception just telling the amount was undefined.

[Roland van Ipenburg]

The vague error goes away if we replace undefined with $EMPTY, but we don’t know if that is the way to go.

[Roland van Ipenburg]

It looks like the constructor of Moose always requires a hashref or a list of key-value pairs as arguments after the instance argument.