gistfile1.txt

test_json_values.new(j_field => ${:foo(1)}, k_val => Any)
{foo => 1}
test_json_values.new(j_field => Any, k_val => ${:foo(1)})
(Any)
Use of uninitialized value element of type Any in string context.
Methods .^name, .raku, .gist, or .say can be used to stringify it to something meaningful.
  in sub from-json at /Users/samuel/.rakubrew/versions/moar-2021.12/install/share/perl6/site/sources/EA6CA341123ECF37C6657DBCBE16F4B077343BB6 (JSON::Fast) line 722
test_json_values.new(j_field => Any, k_val => ${:foo(Any)})
(Any)

Models.rakumod

model test_json_values is table<test_json_values> is export {
    has Json $.j_field is column;
    has Json $.k_val is column;
}

sub fetch-nullable-json-values() is export {
    for test_json_values.^all -> $val {
	  say $val;
	  say $val.j_field;
    }
}

test.sql

--
-- > select * from test_json_values;
--     j_field   |     k_val
--  -------------+----------------
--   {"foo" : 1} |
--               | {"foo" : 1}
--               | {"foo" : null}