refactor: reset last list used to default rather than NULL

Author: AlexanderBlanchardAC

code/cron/src/com/turning_leaf_technologies/cron/DatabaseCleanup.java

@@ -454,7 +454,7 @@ private void removeOldLastListUsed(Connection dbConn, Logger logger, CronProcess
 			//Get list of libraries that want last used list cleared
 			PreparedStatement librariesListStmt = dbConn.prepareStatement("SELECT libraryId FROM library WHERE deleteLastListUsedEntries = 1");
 			PreparedStatement libraryLocationsStmt = dbConn.prepareStatement("SELECT locationId FROM location where libraryId = ?");
-			PreparedStatement deleteLastListUsedStmt = dbConn.prepareStatement("UPDATE user SET lastListUsed = NULL WHERE lastListUsed = ?");
+			PreparedStatement deleteLastListUsedStmt = dbConn.prepareStatement("UPDATE user SET lastListUsed = -1 WHERE lastListUsed = ?");
 
 			ResultSet librariesListRS = librariesListStmt.executeQuery();