```sql
CREATE TABLE test_tbl
(   `ip` String, `ipv6` IPv6 MATERIALIZED toIPv6(ip) )
ENGINE = Memory;

insert into test_tbl(ip) values ( 'fe80::9801:43ff:fe1f:7690'), ('1.1.1.1'), (''), ('::ffff:1.1.1.1' );

 DB::Exception: Invalid IPv6 value: while executing 'FUNCTION _CAST(toIPv6(ip) :: 2, 'IPv6' :: 1)


set cast_ipv4_ipv6_default_on_conversion_error=1;
insert into test_tbl(ip) values ( 'fe80::9801:43ff:fe1f:7690'), ('1.1.1.1'), (''), ('::ffff:1.1.1.1' );
 
 DB::Exception: Invalid IPv6 value: while executing 'FUNCTION _CAST(toIPv6(ip)
```

`toIPv6OrDefault` does not help in this case.

```sql
CREATE TABLE test_tbl
(   `ip` String, `ipv6` IPv6 MATERIALIZED toIPv6OrDefault(ip) )
ENGINE = Memory;

insert into test_tbl(ip) values ( 'fe80::9801:43ff:fe1f:7690'), ('1.1.1.1'), (''), ('::ffff:1.1.1.1' );
  DB::Exception: Invalid IPv6 value: while executing 'FUNCTION _CAST(toIPv6OrD

insert into test_tbl(ip) values ( 'fe80::9801:43ff:fe1f:7690'), ('1.1.1.1'), (''), ('::ffff:1.1.1.1' ), ('garbudge');
  DB::Exception: Invalid IPv6 value: while executing 'FUNCTION
```

WA:

```sql
CREATE TABLE test_tbl
(   `ip` String, `ipv6` IPv6 MATERIALIZED if(ip='', '::', ip) )
ENGINE = Memory;

insert into test_tbl(ip) values ( 'fe80::9801:43ff:fe1f:7690'), ('1.1.1.1'), (''), ('::ffff:1.1.1.1' );

select ip, ipv6 from test_tbl;
┌─ip────────────────────────┬─ipv6──────────────────────┐
│ fe80::9801:43ff:fe1f:7690 │ fe80::9801:43ff:fe1f:7690 │
│ 1.1.1.1                   │ ::ffff:1.1.1.1            │
│                           │ ::                        │
│ ::ffff:1.1.1.1            │ ::ffff:1.1.1.1            │
└───────────────────────────┴───────────────────────────┘
```
\
    M(Bool, join_use_nulls, false, "Use NULLs for non-joined rows of outer JOINs for types that can be inside Nullable. If false, use default value of corresponding columns data type.", IMPORTANT) \
    \
    M(JoinStrictness, join_default_strictness, JoinStrictness::ALL, "Set default strictness in JOIN query. Possible values: empty string, 'ANY', 'ALL'. If empty, query without strictness will throw exception.", 0) \
    M(Bool, any_join_distinct_right_table_keys, false, "Enable old ANY JOIN logic with many-to-one left-to-right table keys mapping for all ANY JOINs. It leads to confusing not equal results for 't1 ANY LEFT JOIN t2' and 't2 ANY RIGHT JOIN t1'. ANY RIGHT JOIN needs one-to-many keys mapping to be consistent with LEFT one.", IMPORTANT) \
    \
    M(UInt64, preferred_block_size_bytes, 1000000, "", 0) \
    \
    M(UInt64, max_replica_delay_for_distributed_queries, 300, "If set, distributed queries of Replicated tables will choose servers with replication delay in seconds less than the specified value (not inclusive). Zero means do not take delay into account.", 0) \
    M(Bool, fallback_to_stale_replicas_for_distributed_queries, true, "Suppose max_replica_delay_for_distributed_queries is set and all replicas for the queried table are stale. If this setting is enabled, the query will be performed anyway, otherwise the error will be reported.", 0) \
    M(UInt64, preferred_max_column_in_block_size_bytes, 0, "Limit on max column size in block while reading. Helps to decrease cache misses count. Should be close to L2 cache size.", 0) \
    \
    M(Bool, insert_distributed_sync, false, "If setting is enabled, insert query into distributed waits until data will be sent to all nodes in cluster.", 0) \
    M(UInt64, insert_distributed_timeout, 0, "Timeout for insert query into distributed. Setting is used only with insert_distributed_sync enabled. Zero value means no timeout.", 0) \
    M(Int64, distributed_ddl_task_timeout, 180, "Timeout for DDL query responses from all hosts in cluster. If a ddl request has not been performed on all hosts, a response will contain a timeout error and a request will be executed in an async mode. Negative value means infinite. Zero means async mode.", 0) \
    M(Milliseconds, stream_flush_interval_ms, 7500, "Timeout for flushing data from streaming storages.", 0) \
    M(Milliseconds, stream_poll_timeout_ms, 500, "Timeout for polling data from/to streaming storages.", 0) \
    \
    /** Settings for testing hedged requests */ \
    M(Milliseconds, sleep_in_send_tables_status_ms, 0, "Time to sleep in sending tables status response in TCPHandler", 0) \
    M(Milliseconds, sleep_in_send_data_ms, 0, "Time to sleep in sending data in TCPHandler", 0) \
    M(UInt64, unknown_packet_in_send_data, 0, "Send unknown packet instead of data Nth data packet", 0) \
    /** Settings for testing connection collector */ \
    M(Milliseconds, sleep_in_receive_cancel_ms, 0, "Time to sleep in receiving cancel in TCPHandler", 0) \
    \
    M(Bool, insert_allow_materialized_columns, false, "If setting is enabled, Allow materialized columns in INSERT.", 0) \
    M(Seconds, http_connection_timeout, DEFAULT_HTTP_READ_BUFFER_CONNECTION_TIMEOUT, "HTTP connection timeout.", 0) \
    M(Seconds, http_send_timeout, DEFAULT_HTTP_READ_BUFFER_TIMEOUT, "HTTP send timeout", 0) \
    M(Seconds, http_receive_timeout, DEFAULT_HTTP_READ_BUFFER_TIMEOUT, "HTTP receive timeout", 0) \
    M(UInt64, http_max_uri_size, 1048576, "Maximum URI length of HTTP request", 0) \