Imports
- github.com/golang/protobuf/proto
- github.com/golang/protobuf/ptypes/empty
- github.com/golang/protobuf/ptypes/timestamp
- golang.org/x/net/context
- google.golang.org/genproto/googleapis/spanner/v1
- google.golang.org/grpc
- google.golang.org/grpc/codes
- google.golang.org/grpc/status
- github.com/golang/protobuf/ptypes/struct