ERROR message at the bottom of kie-server swagger docs page

When opened http://localhost:8080/kie-server/docs/ , we see "ERROR" icon at the bottom of the page. If we press it, it connects to https://online.swagger.io/validator/debug?url=../services/rest/server/swagger.json and response is

{"schemaValidationMessages":[{"level":"error","message":"Can't read from file ../services/rest/server/swagger.json"}]}

See attached swagger-error.png