old_contents: from abc import ABCMeta, abstractmethod
  from io import StringIO
  from typing import Optional, TextIO
  
  
  class Serializable(metaclass=ABCMeta):
  
      @abstractmethod
      def serialize(self, file: TextIO) -> Optional[str]:
          """
          Write the object to provided text file object as MSD.
          """
          pass
      
      def __str__(self):
          """
          Convert the object to an MSD string.
          """
          serialized = StringIO()
          self.serialize(serialized)
          return serialized.getvalue()
new_contents: from abc import ABCMeta, abstractmethod
  from io import StringIO
  from typing import Optional, TextIO
  
  
  class Serializable(metaclass=ABCMeta):
  
      @abstractmethod
      def serialize(self, file: TextIO) -> None:
          """
          Write the object to provided text file object as MSD.
          """
          pass
      
      def __str__(self):
          """
          Convert the object to an MSD string.
          """
          serialized = StringIO()
          self.serialize(serialized)
          return serialized.getvalue()
subject: remove Serializable.serialize return type