If you define a primary column, the attribute notnull is removed from the column definition because Doctrine assumes that primary columns are always not null.
Now suppose you have a schema like this, with a string primary column.
That's fine, but causes problems with MySQL where the column is created with a default value of "" (empty string) and not <none>.
Note that the 2nd column is well defined and has <none> as default value (as seen from phpMyAdmin).
I attached a quick-workaround to disable the code which removes the notnull attribute from column definition.
After that the SQL code is like this: