[BUG][JAVA] Generated model with generics doesn't compile with escaped code

Description

In my OpenAPI specification I have an object:

    WithUnknownData:
      type: object
      title: WithUnknownData
      x-internal: true
      properties:
        data:
          oneOf:
            - type: object
            - type: array
              items: {}

I configured the generator to generate a Java client:

{
        "generatorName": "java",
        "inputSpec": "docs/openapi.yaml",
        "output": "generated-clients/java"
      }

When I look at the generated model, I get:

public class WithUnknownData {
  public static final String SERIALIZED_NAME_DATA = "data";
  @SerializedName(SERIALIZED_NAME_DATA)
  private WithUnknownDataData data;

  public WithUnknownData() {
  }

  public WithUnknownData data(WithUnknownDataData data) {
    
    this.data = data;
    return this;
  }
/* And more code*/
}

When I drill down to WithUnknownDataData I see it does not compile, because some of the generated code is escaped:

public static class CustomTypeAdapterFactory implements TypeAdapterFactory {
        @SuppressWarnings("unchecked")
        @Override
        public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
            if (!WithUnknownDataData.class.isAssignableFrom(type.getRawType())) {
                return null; // this class only serializes 'WithUnknownDataData' and its subtypes
            }
            final TypeAdapter<JsonElement> elementAdapter = gson.getAdapter(JsonElement.class);
            final TypeAdapter<List&lt;Object&gt;> adapterList&lt;Object&gt; = gson.getDelegateAdapter(this, TypeToken.get(List&lt;Object&gt;.class));
            final TypeAdapter<Object> adapterObject = gson.getDelegateAdapter(this, TypeToken.get(Object.class));

            return (TypeAdapter<T>) new TypeAdapter<WithUnknownDataData>() {
                @Override
                public void write(JsonWriter out, WithUnknownDataData value) throws IOException {
                    if (value == null || value.getActualInstance() == null) {
                        elementAdapter.write(out, null);
                        return;
                    }

                    // check if the actual instance is of the type `List&lt;Object&gt;`
                    if (value.getActualInstance() instanceof List&lt;Object&gt;) {
                        JsonObject obj = adapterList&lt;Object&gt;.toJsonTree((List&lt;Object&gt;)value.getActualInstance()).getAsJsonObject();
                        elementAdapter.write(out, obj);
                        return;
                    }

                    // check if the actual instance is of the type `Object`
                    if (value.getActualInstance() instanceof Object) {
                        JsonObject obj = adapterObject.toJsonTree((Object)value.getActualInstance()).getAsJsonObject();
                        elementAdapter.write(out, obj);
                        return;
                    }

                    throw new IOException("Failed to serialize as the type doesn't match oneOf schemas: List<Object>, Object");
                }

                @Override
                public WithUnknownDataData read(JsonReader in) throws IOException {
                    Object deserialized = null;
                    JsonObject jsonObject = elementAdapter.read(in).getAsJsonObject();

                    int match = 0;
                    ArrayList<String> errorMessages = new ArrayList<>();
                    TypeAdapter actualAdapter = elementAdapter;

                    // deserialize List<Object>
                    try {
                        // validate the JSON object to see if any exception is thrown
                        List&lt;Object&gt;.validateJsonObject(jsonObject);
                        actualAdapter = adapterList&lt;Object&gt;;
                        match++;
                        log.log(Level.FINER, "Input data matches schema 'List<Object>'");
                    } catch (Exception e) {
                        // deserialization failed, continue
                        errorMessages.add(String.format("Deserialization for List<Object> failed with `%s`.", e.getMessage()));
                        log.log(Level.FINER, "Input data does not match schema 'List<Object>'", e);
                    }

                    // deserialize Object
                    try {
                        // validate the JSON object to see if any exception is thrown
                        Object.validateJsonObject(jsonObject);
                        actualAdapter = adapterObject;
                        match++;
                        log.log(Level.FINER, "Input data matches schema 'Object'");
                    } catch (Exception e) {
                        // deserialization failed, continue
                        errorMessages.add(String.format("Deserialization for Object failed with `%s`.", e.getMessage()));
                        log.log(Level.FINER, "Input data does not match schema 'Object'", e);
                    }

                    if (match == 1) {
                        WithUnknownDataData ret = new WithUnknownDataData();
                        ret.setActualInstance(actualAdapter.fromJsonTree(jsonObject));
                        return ret;
                    }

                    throw new IOException(String.format("Failed deserialization for WithUnknownDataData: %d classes match result, expected 1. Detailed failure message for oneOf schemas: %s. JSON: %s", match, errorMessages, jsonObject.toString()));
                }
            }.nullSafe();
        }
    }

As you can see some the code looks like this:
final TypeAdapter<List**<Object>> adapterList<Object>**

I tried all sorts of additional properties hoping they would solve this issue, but nothing worked.

openapi-generator version

6.6.0

OpenAPI declaration file content or url

    WithUnknownData:
      type: object
      title: WithUnknownData
      x-internal: true
      properties:
        data:
          oneOf:
            - type: object
            - type: array
              items: {}

Generation Details

{
"generatorName": "java",
"inputSpec": "docs/openapi.yaml",
"output": "generated-clients/java"
}

Steps to reproduce

Related issues/PRs

Suggest a fix

Reproduce the issue with the supplied OpenAPI schema and Java generator configuration from version 6.6.0. Inspect the generated WithUnknownDataData source and the Java generation path that produces its escaped generic types. Done means the generated Java model compiles with the affected schema.