It seems to raise a perfectly valid exception for me
Well, a Perl-generated warning is not the same as a program-generated exception, and here we have only a Perl-generated warning.

In reply to Re^2: Math::Round::Var::round() takes no action when a number is not supplied by metaperl
in thread Math::Round::Var::round() takes no action when a number is not supplied by metaperl

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