No binary data from UNION ALL

[aschnappauf]

Using UNION ALL with SELECT-Statements containing binary (BLOB-Type) columns yields the expected result. However, if one SELECT specifies a NULL or empty bianry value (UNHEX("")), The resulting column will contain NULL for all values.

That is, two tables:

CREATE TABLE a(name VARCHAR(255), data BLOB);
CREATE TABLE b(name VARCHAR(255), data BLOB);

INSERT INTO a VALEUS ("a-data", UNHEX("deadbeef"));
INSERT INTO b VALEUS ("b-nodata", NULL);

SELECT name, data FROM a
UNION ALL
SELECT name, data FROM b;

/* Correct, yields
a-data   | <binary>
b-nodata | NULL
*/

SELECT name, data FROM a
UNION ALL
SELECT name, NULL FROM b;

/* Incorrect, yields
a-data   | NULL
b-nodata | NULL
*/

SELECT name, data FROM a
UNION ALL
SELECT name, UNHEX("") FROM b;

/* Incorrect, yields
a-data   | NULL
b-nodata | 
*/

A live example can be viewed at aschnappauf/view-union-blob-bug at DoltHub. There are three views demonstrating the bug. All three views should yield the same result for rows of tablename and tablename2