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  # assuming $obj->{attr_name} holds a hashref
  return $obj->{attr_name};
...
# code passes

foreach my $item (keys %{ $obj->method() }) {

my %hash    = qw(foo bar baz quux);
my $hashref = \%hash;
...
keys %{{@$listref}}; # valid
keys $hashref;       # invalid
keys %{@list};       # invalid