I would assume that somewhere in MooseX::Types, it is declared how to pass an instance of a type or undef. Other languages use a Maybe(Str) construct for that, but I don't know what the Moose people believe should be used. Moose::Util::TypeConstraints claim that there is Maybe[`a], so maybe that's what you should use:

Maybe[Str] $foo

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In reply to Re: Passing Str or undef ? by Corion
in thread Passing Str or undef ? by John M. Dlugosz

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