old_contents: '''Backend exception hierarchy'''
  
  
  class BackendError(Exception):
      '''Base exception for all problems with the backend.'''
      pass
  
  
  class BadTypeError(BackendError):
      pass
  
  
  class TimeOrderError(BackendError):
      pass
  
  
  class SeriesCreationError(BackendError):
      pass
  
  
  class SeriesDoesNotExistError(BackendError):
      pass
  
  
  class SeriesTimeOrderError(BackendError):
      pass
  
new_contents: '''Backend exception hierarchy'''
  
  
  class BackendError(Exception):
      '''Base exception for all problems with the backend.'''
      pass
  
  
  class BadTypeError(BackendError):
      pass
  
  
  class BadSelectorError(BackendError):
      pass
  
  
  class TimeOrderError(BackendError):
      pass
  
  
  class SeriesCreationError(BackendError):
      pass
  
  
  class SeriesDoesNotExistError(BackendError):
      pass
  
  
  class SeriesTimeOrderError(BackendError):
      pass
  
subject: Add exception for selector errors