XMLDB: Check defaults does not work correctly with char fields

1 On a fresh Moodle install (for example one generated for Behat testing), go to admin / development / xmldb and run the 'Check defaults' script EXPECTED: There should be no incorrect defaults 2 Make changes to a database table so that it has an incorrect default. These commands work in Postgres, but different variants are needed for other database(s): – default where previous default was blank ALTER TABLE mdl_course_categories ALTER COLUMN name SET DEFAULT 'Kermit'; – default where previously no default ALTER TABLE mdl_course_categories ALTER COLUMN idnumber SET DEFAULT '001'; – no default where previously default ALTER TABLE mdl_course_categories ALTER COLUMN path DROP DEFAULT; – different default compared to previous default ALTER TABLE mdl_course_categories ALTER COLUMN visible SET DEFAULT 42; 3 Purge all caches 4 Rerun the check defaults EXPECTED: There should now be 4 incorrect defaults shown: Table: course_categories. Field: name, Expected '' Actual 'Kermit' Table: course_categories. Field: idnumber, Expected - Actual '001' Table: course_categories. Field: visible, Expected '1' Actual '42' Table: course_categories. Field: path, Expected '' Actual - NOTE: The SQL commands below are not complete ('path' is not included), I guess this is a separate bug but I didn't want to change this bit because the logic used to generate those is also used for actually doing things not just this check script!