docs: def get_consensus_at(self, block_id):
          """
          Get the consensus hash at a given block.
          Return the consensus hash if we have one for this block.
          Return None if we don't
          """
          query = 'SELECT consensus_hash FROM snapshots WHERE block_id = ?;'
          args = (block_id,)
  
          con = self.db_open(self.impl, self.working_dir)
          rows = self.db_query_execute(con, query, args, verbose=False)
          res = None
  
          for r in rows:
              res = r['consensus_hash']
  
          con.close()
          return res