code: func (t *Transaction) RetrieveHash(ns string, coll string) []byte {
  	if t.RWSet == nil {
  		return nil
  	}
  	for _, nsData := range t.RWSet.NsRwSets {
  		if nsData.NameSpace != ns {
  			continue
  		}
  
  		for _, collData := range nsData.CollHashedRwSets {
  			if collData.CollectionName == coll {
  				return collData.PvtRwSetHash
  			}
  		}
  	}
  	return nil
  }
docs: // RetrieveHash returns the hash of the private write-set present
  // in the public data for a given namespace-collection