my %hash = (
            'key1' => 'value1',
            'key2' => scalar $r->param('doesnt_exist'),
            'key3' => 'value3',
);

##</code><code>##

my %hash = (
            'key1' => 'value1',
            'key2' => [ $r->param('multi_valued') ],
            'key3' => 'value3',
);