$ perl -MData::Dumper -Mstrict -wE 'my $foo = {}; say for @{ $foo->{bar} }; say Dumper $foo'
$VAR1 = {
          'bar' => []
        };

##</code><code>##

$ perl -MData::Dumper -Mstrict -wE 'my $foo = {}; say for @{ $foo->{bar} // [] }; say Dumper $foo'
$VAR1 = {};

##</code><code>##

    open(my $fh, '<', "$file_path") or return 0;

    my $href = {};

    while (my $line = <$fh>) {
    
        # ...........
        # ...........
        # Additional operations of the lines of the file
        # ...........
        # ...........
        
        push @{ $href->{test} }, {
            group  => $group,
            values => [ sort uniq $value, @{ $href->{values} // [] } ],
        };
    }