use warnings;
use diagnostics;

##</code><code>##

use strict;
use warnings;
use diagnostics;

my $href;
my %hash;

%hash = %{$href};

--Error--
Can't use an undefined value as a HASH reference at line 8 (#1)
    (F) A value used as either a hard reference or a symbolic reference must
    be a defined value.  This helps to delurk some insidious errors.
    
Uncaught exception from user code:
	Can't use an undefined value as a HASH reference at line 8.

##</code><code>##

use strict;
use warnings;
use diagnostics;

my $href = {};
my %hash;

%hash = %{$href};

--Error--
This caused no error

##</code><code>##

use strict;
use warnings;
use diagnostics;

my $href;
my %hash;

%hash = %{$href || {}};

--Error--
This caused no error also