code: func (txRwSet *TxRwSet) GetPvtDataHash(ns, coll string) []byte {
  	// we could build and use a map to reduce the number of lookup
  	// in the future call. However, we decided to defer such optimization
  	// due to the following assumptions (mainly to avoid additioan LOC).
  	// we assume that the number of namespaces and collections in a txRWSet
  	// to be very minimal (in a single digit),
  	for _, nsRwSet := range txRwSet.NsRwSets {
  		if nsRwSet.NameSpace != ns {
  			continue
  		}
  		return nsRwSet.getPvtDataHash(coll)
  	}
  	return nil
  }
docs: // GetPvtDataHash returns the PvtRwSetHash for a given namespace and collection