Doc'd TextField.db_collation as optional.
Matches CharField.db_collation docs.
Thanks to Paolo Melchiorre for the report.
@@ -1343,7 +1343,7 @@ However it is not enforced at the model or database level. Use a
.. attribute:: TextField.db_collation
- The database collation name of the field.
+ Optional. The database collation name of the field.
.. note::
