[[JAVA] - Need to generate java.lang.Exception object from Swagger 2.0

I belong to swagger API design team. A Java developer in my team wants me add a CustomException object that extends an Exception object which gets generated as java.lang.Exception object when code is generated using codegen. His argument is that using additionalProperties I was able to generate below code using codegen.

import java.util.Objects;
import java.util.HashMap;
import java.util.Map;
public class RowData extends HashMap<String, Object> {

In the same way he wants me to come up with a way in swagger so that below code is generated by codegen. Please let me know if this is possible in swagger or do we have to manually create this in java class post code generation

import java.lang.Exception;
public class CustomException extends Exception {

Swagger-codegen version

swagger-codegen-cli-2.3.1

Start by reviewing the Swagger 2.0 definition and Java generation behavior in swagger-codegen-cli-2.3.1, then determine whether the generator supports exception inheritance. Done means establishing and documenting a supported way to generate CustomException extending java.lang.Exception, or confirming it must be created manually after generation.