Error message. If non-empty, code generation failed. The plugin process should exit with status code zero even if it reports an error in this way. This should be used to indicate errors in .proto files which prevent the code generator from generating correct code. Errors which indicate a problem in protoc itself -- such as the input CodeGeneratorRequest being unparseable -- should be reported by writing a message to stderr and exiting with a non-zero status code.
Returns a human-readable ASCII format representation of this message.
(Since version 0.6.0) Use toPMessage
(Since version 0.6.0) Use getField that accepts a ScalaPB descriptor and returns PValue