BLOB/TEXT column can't have a default value

if you have a field in table like this:
`f` VARCHAR(200) NOT NULL DEFAULT ' '
and then try to change that to TEXT type -->

SQL Error (1101): BLOB/TEXT column 'f' can't have a default value

Changing should in that case automaticaly assign 'no default value' to that field.

ERROR 1101 (42000) at line 1489: BLOB/TEXT column 'courseids' can't have a default value