Documented behaviour was broken by the patch for bug 33699
that actually is not a bug.
This fix reverts patch for bug 33699 and reverts the
UPDATE of NOT NULL field with NULL query to old
behavior.
columns (default datatype value is assigned).
The mysql_update function has been modified to generate
an error when trying to set a NOT NULL field to NULL rather than a warning
in the set_field_to_null_with_conversions function.