code: def get(self, cond=None, doc_id=None, eid=None):
          
          doc_id = _get_doc_id(doc_id, eid)
  
          # Cannot use process_elements here because we want to return a
          # specific document
  
          if doc_id is not None:
              # Document specified by ID
              return self._read().get(doc_id, None)
  
          # Document specified by condition
          for doc in self.all():
              if cond(doc):
                  return doc
docs: Get exactly one document specified by a query or and ID.
  
          Returns ``None`` if the document doesn't exist
  
          :param cond: the condition to check against
          :type cond: Query
  
          :param doc_id: the document's ID
  
          :returns: the document or None
          :rtype: Element | None