code: func (f *FilterHeaderStore) FetchHeaderByHeight(height uint32) (*chainhash.Hash, error) {
  	// Lock store for read.
  	f.mtx.RLock()
  	defer f.mtx.RUnlock()
  
  	return f.readHeader(height)
  }
docs: // FetchHeaderByHeight returns the filter header for a particular block height.