The new code for normalizing SQL statements and executing them ensured

that the parameters passed in to cursor.execute() was always a

tuple, even if empty. This wasn't correct, since it would trigger an

attempt at string interpolation any time the SQL contained a %

character (such as in a LIKE 'prefix%' condition).
Normally, it'd be up to the caller to either escape the %, or to

provide None as parameters to the statement. These were, in fact,

None, and we were converting tha to an empty tuple. This change

fixes this behavior so that we preserve the type of the parameters

provided by the caller.

Unit tests pass on all supported versions of Django and on all

databases.
Encountered this with the upcoming work on constraint support. Verified

that this no longer triggered crashes executing SQL.