[C++][Pistache-Server] Creation of weird #include statements from oneOf-statement

Description

If I use a schema definition as shown in the yaml-snippet below, I get a file Error.h that contains the following #include statement:
#include OneOfErrInternalErrorErrInvalidIdErrCurrentlyNotAllowedErrApplicationNotLoadableErrApplicationNotAvailableErrItemDoesNotExist.h"
that will never compile because such a file does not exist.
It also contains the following method-declrarations:
OneOfErrInternalErrorErrInvalidIdErrCurrentlyNotAllowedErrApplicationNotLoadableErrApplicationNotAvailableErrItemDoesNotExist getCode() const;
void setCode(OneOfErrInternalErrorErrInvalidIdErrCurrentlyNotAllowedErrApplicationNotLoadableErrApplicationNotAvailableErrItemDoesNotExist const& value);

Neither while validating the yaml that contains this schema does issue an error message nor does the creation process.

openapi-generator version

4.0.0-beta2

OpenAPI declaration file content or url

'''yaml
components:
schemas:
Error:
type: object
required:
- code
- message
properties:
code:
oneOf:
- $ref: '#/components/schemas/ErrInternalError'
- $ref: '#/components/schemas/ErrInvalidId'
- $ref: '#/components/schemas/ErrCurrentlyNotAllowed'
- $ref: '#/components/schemas/ErrApplicationNotLoadable'
- $ref: '#/components/schemas/ErrApplicationNotAvailable'
- $ref: '#/components/schemas/ErrItemDoesNotExist'
message:
type: string
'''

Command line used for generation

java -ea -Xms512M -Xmx1024M -server -jar /home/fili/alpine/gernjo/openAPI/openapi-generator-cli-4.0.0-beta2.jar generate -i ./ontrestapi_device/ore_device.yaml -g cpp-pistache-server -o ./generated_server

Suggest a fix

• Create one include-statement for each of the items listed under oneOf
• Create one specific setter/getter method for each of the items listed under oneOf

Reproduce the issue with the supplied YAML schema and the cpp-pistache-server generation command, then inspect the generated Error.h. Trace how the oneOf entries become the include and accessor type names; done means each referenced schema has valid includes and distinct getter/setter declarations, with generation completing without invalid output.