As mentioned by @obmsch in 0026596:0063437

Difference in generated db schema with mssqlnative driver
custom_field.possible_values
5.20: [text] NULL
5.21: [text] NOT NULL, Default ''

Additional information about the scope of the behavioural changes for BLOBs in ADOdb-5.21 for MantisBT:

1) Only 'X', 'X2', 'XL' and 'B' are affected.
2) The Oracle (oci8) driver 'datadict-oci8.inc.php' is not adjusted(yet).
3) No 'X2' in 'schema.php'.
4) The two 'B's in 'schema.php' (bug_file.content, project_file.content) should be Ok with 'mysql', 'mssql', 'postgres',
as [2] -> [203] and [29] -> [204] anticipate. But 'oci8'?
5) One 'X' in 'schema.php' (need to check).
6) 'XL' should be Ok with 'mysql', 'mssql', 'postgres' (not touched formerly, now handled equally). But 'oci8'?

@dregad This all boils down to [2,4,6] and [5]. No idea about this Oracle stuff, but that should be fixed before 5.21 is released.
I file an issue anyway.

Since this issue was basically a duplicate of 0028015 which is already used as a parent to track ADOdb 5.21 issues, I'm recycling this one to follow-up on BLOB-related stuff reported by @obmsch