## About the changes
Open API code generator does not get along with `oneOf` alongside
`properties`:
```shell
$ openapi-generator-cli validate -i modified-openapi.json --recommend
Validating spec (modified-openapi.json)
Warnings:
- Schemas defining properties and oneOf are not clearly defined in the OpenAPI
Specification. While our tooling supports this, it may cause issues with other tools.
```
bab67e44e4/modules/openapi-generator/src/main/java/org/openapitools/codegen/validations/oas/OpenApiSchemaValidations.java (L25-L29)
This PR adds a meta-schema rule to validate this and fixes one issue
Unless you set `additionalProperties` to `false`, additional properties
are always
allowed. By explicitly setting it to `true` the generated
examples contain additional properties, e.g.:
```json
{
"tokens": [
"aproject:development.randomstring",
"[]:production.randomstring"
],
"additionalProp1": {}
}
```
By removing the explicit annotation, we still allow additional
properties, but we don't get them in examples:
```json
{
"tokens": [
"aproject:development.randomstring",
"[]:production.randomstring"
]
}
```
