code: def migrate_to_blob(context, portal_type, query={}, remove_old_value=True):
      
      migrator = makeMigrator(
          context, portal_type, remove_old_value=remove_old_value)
      walker = BikaCustomQueryWalker(context, migrator, query=query)
      savepoint(optimistic=True)
      walker.go()
      return walker.getOutput()
docs: Migrates FileFields fields to blob ones for a given portal_type.
      The wueries are done against 'portal_catalog', 'uid_catalog' and
      'reference_catalog'
  
      :param context: portal root object as context
      :param query: an expression to filter the catalog by other filters than
      the portal_type.
      :param portal_type: The portal type name the migration is migrating *from*