in reply to no warnings no working while running cgi script under Apache::Registry

It's not a warning, it's an error, to which $@ is set (see perlvar) by eval; $@ seems to be handled by the caller of your code snippet and thrown out STDERR. You get the same error via the command line, if you check for $@ after eval: 
qwurx [shmem] ~ > perl
use strict;
use warnings;

my $class = undef;

eval {  $class->isa('MyClass'); };
warn $@ if $@;
__END__
Can't call method "isa" on an undefined value at - line 6.

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If you want to supress that error, handle $@ yourself after the eval and set it to the empty string ('') after that.

Please wrap any piece of code you post into <code> tags. See Writeup Formatting Tips.

--shmem 

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}

In Section Seekers of Perl Wisdom