1407,1409c1407
< 	my $key = do { local $^W; # silence undef warnings
< 	    join "~~", $dsn, $user||'', $auth||'', $attr ? (@attr_keys,@{$attr}{@attr_keys}) : ()
< 	};
---
> 	my $key = join "~~", $dsn, $user||'', $auth||'', map { defined $_ ? $_ : '' } $attr ? ( @attr_keys, @{$attr}{@attr_keys} ) : ();