$ perl -w
$self->{$Foo}{$Bar} = $self->{$Baz}{undef}->method;
^Z
Name "main::Baz" used only once: possible typo at - line 1.
Name "main::Bar" used only once: possible typo at - line 1.
Name "main::Foo" used only once: possible typo at - line 1.
Use of uninitialized value $Baz in hash element at - line 1.
Can't call method "method" on an undefined value at - line 1.