OpenAPI Generator: How to fix WARN o.o.codegen.DefaultCodegen - The value (generator's option) must be either boolean or string. Default to `false`

I am using the following OpenAPI commands to generate client using openapi-generator:

npx @openapitools/openapi-generator-cli generate -i api.yaml -g cpp-restsdk -o  %CD%

after running the command why it shows the following warning:

[main] WARN  o.o.codegen.DefaultCodegen - The value (generator's option) must be either boolean or string. Default to `false`.