To your first question:
If you assign () to a scalar variable, the value of that variable will be undef.
Why it seems to be different in array assingment, I don't know.

To your second question:
The shortest undef is $\, which is undef by default.

In reply to Re: Collapsing Arrays with Empty Values by busunsl
in thread Collapsing Arrays with Empty Values by tadman

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