Invalid code generated for missing discriminator property, but validation passes

Reproduce the issue with test2.json and rpdmcpp.config by running the shown validate and generate commands, then inspect the generated Base.java. Trace the validation path for the discriminator property; done means validation reports the missing property instead of accepting the spec that produces non-compiling Java code.

Description

A spec with missing discriminator property passes validation, but generates invalid (Java) code.

openapi-generator version

3.3.0-SNAPSHOT

OpenAPI declaration file content or url

{
    "openapi": "3.0.0",
    "info": {
        "description": "blah",
        "version": "1.0.0",
        "title": "blah"
    },
    "paths": {
        "/test": {
            "post": {
                "tags": [
                  "test"
                ],
                "operationId": "testOp",
                "responses": {
                    "405": {
                        "description": "Invalid input"
                    }
                },
                "requestBody": {
                    "$ref": "#/components/requestBodies/Test"
                }
            }
        }
    },
    "components": {
        "requestBodies": {
            "Test": {
                "content": {
                    "application/json": {
                        "schema": {
                            "$ref": "#/components/schemas/Test"
                        }
                    }
                }
            }
        },
        "schemas": {
            "Base": {
                "properties": {
                    "status": {
                        "type": "string"
                    }
                },
                "discriminator":{
                    "propertyName": "type"
                }
            },
            "Test": {
                "allOf":[
                    { "$ref": "#/components/schemas/Base" },
                    {
                        "type":"object",
                        "properties": {
                            "name": {
                                "type": "string"
                            }
                        }
                    }
                ]
            }
        }
    }
}

rpdmcpp.config is

{
	"declspec" : "DL_GLOBAL_CLASS",
	"appName" : "RPDM",
	"appDescription" : "RedPoint Data Management services"
}

Command line used for generation

Validate succeeds

java -cp openapi-generator-cli.jar org.openapitools.codegen.OpenAPIGenerator validate -i test2.json
Validating spec (test2.json)
No validation issues detected.

But java code generation:
java -cp openapi-generator-cli.jar org.openapitools.codegen.OpenAPIGenerator generate -v -o genjava -g java -i test2.json -c rpdmcpp.config
produces non-compiling code. The problem is that the type field is not defined. In Base.java:

  public Base() {
    this.type = this.getClass().getSimpleName();
  }

Suggest a fix/enhancement

Validation should flag the spec as being in error.