docs: def database_current_migration(self):
          """
          Return the current migration in the database.
          """
          # If the table doesn't even exist, return None.
          if not self.migration_table.exists(self.session.bind):
              return None
  
          # Also return None if self.migration_data is None.
          if self.migration_data is None:
              return None
  
          return self.migration_data.version