old_contents: __author__ = 'George Oblapenko, Viktor Evstratov'
  __license__ = "GPLv3"
  # Custom erros (no backend found, no such id, cannot add to db, field with this name already exists, etc) go here
  
  
  class UnsupportedOperation(Exception):
      pass
  
  
  class OverwriteError(Exception):
      pass
  
  
  class UnknownBackend(Exception):
      pass
  
  
  class DoesNotExist(Exception):
      pass
  
  
  class DataPropertyNameCollision(Exception):
      pass
  
  
  class ProtectedField(Exception):
      pass
  
  
  class KrakenlibException(Exception):
      pass
new_contents: __author__ = 'George Oblapenko, Viktor Evstratov'
  __license__ = "GPLv3"
  # Custom erros (no backend found, no such id, cannot add to db, field with this name already exists, etc) go here
  
  
  class UnsupportedOperation(Exception):
      pass
  
  
  class OverwriteError(Exception):
      pass
  
  
  class UnknownBackend(Exception):
      pass
  
  
  class DoesNotExist(Exception):
      pass
  
  
  class DataPropertyNameCollision(Exception):
      pass
  
  
  class ProtectedField(Exception):
      pass
  
  
  class KrakenlibException(Exception):
      pass
  
  
  class EmptyDataSet(Exception):
      pass
subject: check if dataset is empty, raise error otherwise