COALESCE() returns nullable column while IFNULL() does not — unexpected behavior in VIEW definition

-- Setup

CREATE OR REPLACE VIEW test_coalesce_vs_ifnull AS

SELECT

  -- Nullable column fallback via COALESCE()

  COALESCE(operation_date, '1970-01-01 00:00:00') AS coalesced_date,

  -- Nullable column fallback via IFNULL()

  IFNULL(operation_date, '1970-01-01 00:00:00') AS ifnull_date

FROM (

  SELECT NULL AS operation_date

) AS t;

SELECT COLUMN_NAME, IS_NULLABLE, COLUMN_TYPE

FROM INFORMATION_SCHEMA.COLUMNS

WHERE TABLE_NAME = 'test_coalesce_vs_ifnull';

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

| COLUMN_NAME     | IS_NULLABLE | COLUMN_TYPE |

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

| coalesced_date  | YES         | varchar(19) |

| ifnull_date     | NO          | varchar(19) |

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