docs: def add(self, documents, boost=None):
          """
          Adds documents to Solr index
          documents - Single item or list of items to add
          """
  
          if not isinstance(documents, list):
              documents = [documents]
          documents = [{'doc': d} for d in documents]
          if boost:
              for d in documents:
                  d['boost'] = boost
  
          self._add_batch.extend(documents)
  
          if len(self._add_batch) > SOLR_ADD_BATCH:
              self._addFlushBatch()