Here are different ways to create an empty hash named "hash".

my %hash;
my %hash = ();

Keys that contain no values (empty keys) can be created like this.

%hash = (
  name_key => "", 
  id_key => "", 
  department_key => ""
);

Or, like this.

$hash{name_key}       = undef;
$hash{id_key}         = undef;
$hash{department_key} = undef;

Or, like this.

$hash{name_key}       = "";
$hash{id_key}         = "";
$hash{department_key} = "";

Dumper can be used to display the structure of the hash.

use Data::Dumper;
print Dumper \%hash;

Which will display the data structure of the hash.

$VAR1 = {
           'name_key' => '',
           'id_key' => '',
           'department_key' => ''
        };