old_contents: 
  
  class CaseRelationshipError(Exception):
  
      def __init__(self, message, child_case_id, child_case_type, identifier, relationship, num_related_found):
          self.child_case_id = child_case_id
          self.child_case_type = child_case_type
          self.identifier = identifier
          self.relationship = relationship
          self.num_related_found = num_related_found
  
          super(CaseRelationshipError, self).__init__(message)
  
new_contents: from __future__ import absolute_import
  from __future__ import unicode_literals
  
  
  class CaseRelationshipError(Exception):
  
      def __init__(self, message, child_case_id, child_case_type, identifier, relationship, num_related_found):
          self.child_case_id = child_case_id
          self.child_case_type = child_case_type
          self.identifier = identifier
          self.relationship = relationship
          self.num_related_found = num_related_found
  
          super(CaseRelationshipError, self).__init__(message)
  
subject: add missing imports