code: def invalidate_config_var_entry(self, index):
          
  
          if index == 0 or index > len(self.config_database.entries):
              return [Error.INVALID_ARRAY_KEY, b'']
  
          entry = self.config_database.entries[index - 1]
          if not entry.valid:
              return [ConfigDatabaseError.OBSOLETE_ENTRY, b'']
  
          entry.valid = False
          return [Error.NO_ERROR]
docs: Mark a config variable as invalid.