MariaDB [test]> select CAST(1 as unsigned) union all select NULL;

Field   1:  `CAST(1 as unsigned)`

Catalog:    `def`

Database:   ``

Table:      ``

Org_table:  ``

Type:       NEWDECIMAL

Collation:  binary (63)

Length:     2

Max_length: 1

Decimals:   0

Flags:      BINARY NUM 

+---------------------+

| CAST(1 as unsigned) |

+---------------------+

|                   1 |

|                NULL |

+---------------------+

2 rows in set (0.000 sec)

MariaDB [test]> select CAST(1 as unsigned) union all select * from (select NULL) t;

Field   1:  `CAST(1 as unsigned)`

Catalog:    `def`

Database:   ``

Table:      ``

Org_table:  ``

Type:       NEWDECIMAL

Collation:  binary (63)

Length:     42

Max_length: 40

Decimals:   39

Flags:      BINARY NUM 

+------------------------------------------+

| CAST(1 as unsigned)                      |

+------------------------------------------+

| 1.00000000000000000000000000000000000000 |

|                                     NULL |

+------------------------------------------+

2 rows in set (0.000 sec)