Update an internal Data-group

hello,

now, i can update the Datagroup, but i can't add some data.

sub modif_datagroup {
    my ($bigip, $datagroup) = @_;
    my $json = '{"name":"test1","records":"test1"}';

    $bigip->PATCH('ltm/data-group/internal/~Common~'. $datagroup, $json);
}

When i list the all properties, i have this :

(tmos) list ltm data-group internal my-datagroup all-properties 
    ltm data-group internal my-datagroup {
        app-service none
        description none
        partition Common
        records {
            test1 {
                data none
            }
        }
        type string
    }

Someone can explain me how i can add a data in datagroup ?