JSON schema of imported files are not generated

I have two files: `proto_x.proto` and `imported.proto`, `proto_x.proto` has `import imported.proto`.

When I use compiler CLI with the following options: `proto_x.proto -g=html -I=src/input -o=src/output`, there is no JSON schema of `imported.proto` was genererated into `src/output/data/type`.

Did I configure something wrong? Thank you for checking out.