[BUG][Java/Spring] additionalProperties to true breaks compilation

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

v5.0.0-beta2 and v5.0.0-beta3 do not generate correct Java putPropertiesItem method for Map fields

openapi-generator version

v5.0.0-beta2, v5.0.0-beta3 and latest

Works ok in v5.0.0-beta

OpenAPI declaration file content or url

openapi: 3.0.3
info:
  title: Test
  version: '1.0.0'

paths:
  /test:
    get:
      summary: Test
      description: Example
      responses:
        200:
          description: Successful response
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/test'

components:
  schemas:
    test:
      type: object
      required:
        - field_A
        - field_B
      properties:
        field_A:
          type: string
          enum:
            - Feature
        field_B:
          type: integer
        properties:
          type: object
          properties:
            field_C:
              type: integer
          additionalProperties: true

Generation Details

cat out/java/src/main/java/org/openapitools/model/Test.java
Expected

  public Test putPropertiesItem(String key, Object propertiesItem) {
    if (this.properties == null) {
      this.properties = new HashMap<>();
    }
    this.properties.put(key, propertiesItem);
    return this;
  }

vs

  public Test putPropertiesItem(String key, Object propertiesItem) {
    if (this.properties == null) {
      this.properties = ;
    }
    this.properties.put(key, propertiesItem);
    return this;
  }

Steps to reproduce

docker run --rm \                                          
    -v $PWD:/local openapitools/openapi-generator-cli:v5.0.0-beta3 generate \ 
    -i /local/test.yaml \
    -g spring \
    -o /local/out/java

Related issues/PRs

Suggest a fix

Reproduce the issue with the supplied OpenAPI YAML and the documented Docker command using the spring generator, then inspect the generated out/java/src/main/java/org/openapitools/model/Test.java. Trace how additionalProperties: true produces putPropertiesItem and verify the generated project compiles with the expected HashMap initialization.