code: func NewStreamsByType() map[OperationType]map[uint64]*Stream {
  	m := make(map[OperationType]map[uint64]*Stream)
  	m[ConsensusOperation] = make(map[uint64]*Stream)
  	m[SubmitOperation] = make(map[uint64]*Stream)
  	return m
  }
docs: // NewStreamsByType returns a mapping of operation type to
  // a mapping of destination to stream.