[ALL] System properties no longer working properly

Description

I'm currently trying to adopt Swagger Codegen 3.0 and noticed that specifying system properties with -D is strangely broken.

More specifically: Executing Codegen 3.0.3 with -Dapis -Dmodel only generates the models but no longer the apis. The same works fine in Codegen 2.3.1.

Swagger-codegen version

The problem exists in 3.0.3. It does not exists in 2.3.1.

Swagger declaration file content or url

Doesn't matter. I've used the PetStore example: https://petstore.swagger.io/v2/swagger.yaml

Steps to reproduce

1. Get Codegen 2.3.1: http://central.maven.org/maven2/io/swagger/swagger-codegen-cli/2.3.1/swagger-codegen-cli-2.3.1.jar
2. Get Codegen 3.0.3: http://central.maven.org/maven2/io/swagger/codegen/v3/swagger-codegen-cli/3.0.3/swagger-codegen-cli-3.0.3.jar
3. Store PetStore.yaml in the same directory as petstore.swagger.yaml
4. Generate with 2.3.1: java -cp swagger-codegen-cli-2.3.1.jar io.swagger.codegen.SwaggerCodegen generate --input-spec petstore.swagger.yaml --lang java --output generated/java/v2 -Dapis -Dmodels
5. Generate with 3.0.3: java -cp swagger-codegen-cli-3.0.3.jar io.swagger.codegen.v3.cli.SwaggerCodegen generate --input-spec petstore.swagger.yaml --lang java --output generated/java/v3 -Dapis -Dmodels
6. Notice how the folder (and contents) generated/java/v2/src/main/java/io/swagger/client/api exists while in v3 (generated/java/v3/src/main/java/io/swagger/client/api) it doesn't.

I'm running on Windows 10 with Java 8 (1.8.0_191-b12).

Start with the Java CLI entry points io.swagger.codegen.SwaggerCodegen and io.swagger.codegen.v3.cli.SwaggerCodegen, then reproduce the commands against the PetStore specification using Codegen 2.3.1 and 3.0.3. Trace how -Dapis and -Dmodels are handled; done means the 3.0.3 command generates both API and model output as the older command does.