code: func (hc *HeaderChain) GetHeaderByHash(hash common.Hash) *types.Header {
  	number := hc.GetBlockNumber(hash)
  	if number == nil {
  		return nil
  	}
  	return hc.GetHeader(hash, *number)
  }
docs: // GetHeaderByHash retrieves a block header from the database by hash, caching it if
  // found.