old_contents: from butler_offline.core import FileSystem
  import os
  
  INSTANCE = None
  
  def instance():
      if FileSystem.INSTANCE == None:
          FileSystem.INSTANCE = FileSystemImpl()
      return FileSystem.INSTANCE
  
  
  class FileSystemImpl:
  
      def read(self, file_path):
  
          if not os.path.isfile(file_path):
              return None
  
          file = open(file_path, 'r')
          file_content = []
  
          for line in file:
              file_content.append(line)
  
          file.close()
  
          return file_content
  
      def write(self, file_path, file_content):
          file = open(file_path, 'w')
          file.write(file_content)
          file.close()
  
new_contents: from butler_offline.core import FileSystem
  import os
  
  INSTANCE = None
  
  def instance():
      if FileSystem.INSTANCE == None:
          FileSystem.INSTANCE = FileSystemImpl()
      return FileSystem.INSTANCE
  
  
  class FileSystemImpl:
  
      def read(self, file_path):
  
          if not os.path.isfile(file_path):
              return None
  
          with open(file_path) as file:
              file_content = []
  
              for line in file:
                  file_content.append(line)
          return file_content
  
      def write(self, file_path, file_content):
          with open(file_path, 'w') as file:
              file.write(file_content)
  
subject: move to with open