make gen-rpc失败 'optional' labels are disallowed in the Proto3 syntax

[bendh1]

$ make gen-rpc
goctls rpc protoc ./example.proto --go_out=./types --go-grpc_out=./types --zrpc_out=. --style=go_zero
Generating...
Merge proto files successfully
Error: example.proto:89:12: Explicit 'optional' labels are disallowed in the Proto3 syntax. To define 'optional' fields in Proto3, simply remove the 'optional' label, as fields are 'optional' by default.