Assuming that $foobar isn't undefined you should have a definedness check for the return value of first too. $foobar may be 0 or "".

If undef is allowed as comparision value, use

    defined(
        defined $foobar
        ? first { $_ eq $foobar } @array
        : first { not defined $array[$_] } 0 .. $#array
    )
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ihb