[YCQL] Incorrect TOJSON() output for nested UDT

[OlegLoginov]

Jira Link: DB-7332

Description

The issue:
YB:

ycqlsh:a> create type UDT1 (a int, b int);
ycqlsh:a> create type UDT2 (c int, d frozen<UDT1>);
ycqlsh:a> create table t5 (h int primary key, v UDT2);
ycqlsh:a> insert into t5 (h,v) values (1, {c:1, d:{a:1, b:1}});
ycqlsh:a> select v from t5;
 v
-------------------------
 {c: 1, d: {a: 1, b: 1}}
(1 rows)
ycqlsh:a> select tojson(v) from t5;
 server_tojson(v)
-------------------
 {"c":1,"d":[1,1]}      <<<<< ERROR!
(1 rows)

Cassandra:

cqlsh:a> create type UDT1 (a int, b int);
cqlsh:a> create type UDT2 (c int, d frozen<UDT1>);
cqlsh:a> create table t5 (h int primary key, v UDT2);
cqlsh:a> insert into t5 (h,v) values (1, {c:1, d:{a:1, b:1}});
cqlsh:a> select v from t5;
 v
-------------------------
 {c: 1, d: {a: 1, b: 1}}
(1 rows)
cqlsh:a> select tojson(v) from t5;
 system.tojson(v)
---------------------------------
 {"c": 1, "d": {"a": 1, "b": 1}}       <<<< OK!
(1 rows)

Warning: Please confirm that this issue does not contain any sensitive information

• I confirm this issue does not contain any sensitive information.

[OlegLoginov]

Note that for the first level of nesting it works correctly:
YB:

ycqlsh:a> create type UDT1 (a int, b int);
ycqlsh:a> create table t4 (h int primary key, v UDT1);
ycqlsh:a> insert into t4 (h,v) values (1, {a:1, b:1});
ycqlsh:a> select v from t4;
 v
--------------
 {a: 1, b: 1}
(1 rows)
ycqlsh:a> select tojson(v) from t4;
 server_tojson(v)
------------------
    {"a":1,"b":1}        <<<< OK!
(1 rows)

Cassandra:

cqlsh:a> insert into t4 (h,v) values (1, {a:1, b:1});
cqlsh:a> select v from t4;
 v
--------------
 {a: 1, b: 1}
(1 rows)
cqlsh:a> select tojson(v) from t4;
 system.tojson(v)
------------------
 {"a": 1, "b": 1}        <<< OK
(1 rows)

[OlegLoginov]

Note: The issue affects any UDT< FROZEN<*> > combinations - including UDT< FROZEN<UDT> >, UDT< FROZEN<LIST> >, UDT< FROZEN<SET> >, UDT< FROZEN<MAP> >, etc.