cant get what I want from array_to_json (simple)

CREATE TYPE key_value_pair AS
(key text,
value text);

DO $$declare
arr qsn_app.key_value_pair[];
pcolumn_values_i json;
begin
arr[0] := ('this','that');
arr[1] := ('another','one');
pcolumn_values_i := array_to_json( arr );
RAISE NOTICE '#1 %', pcolumn_values_i;
end$$;

the 'NOTICE' shows:
NOTICE: #1 [{"key":"this","value":"that"},{"key":"another","value":"one"}]
what I want to see is:
NOTICE: #1 {"this":"that","another":"one"}

TIA,
Mike