Openapi-generator-maven-plugin don't generate objects for multipart/form-data request

Question

I am using openapi-generator-maven-plugin for multiple/form-data to upload file with additional data. If I use object (field metadata) in request object wouldn't be generated. For application/json content objects in request are generated. Problem exist only for multipart/form-data content type. Here is my plugin configuration:

<execution>
                    <id>generate rest api interfaces and dtos</id>
                    <phase>generate-resources</phase>
                    <goals>
                        <goal>generate</goal>
                    </goals>
                    <configuration>
                        <inputSpec>${openapi-generator-maven-plugin.inputSpec}</inputSpec>
                        <generatorName>spring</generatorName>
                        <generateSupportingFiles>false</generateSupportingFiles>
                        <modelPackage>${openapi-generator-maven-plugin.modelPackage}</modelPackage>
                        <apiPackage>com.application.api</apiPackage>                            
                        <library>spring-boot</library>
                        <configOptions>
                            <dateLibrary>java8</dateLibrary>
                            <skipDefaultInterface>true</skipDefaultInterface>
                            <useTags>true</useTags>
                        </configOptions>
                    </configuration>
                </execution>

And my api yml config:

/api/document:
put:
  tags:
    - document
  summary: upload
  operationId: upload
  requestBody:
    content:
      multipart/form-data:
        schema:
          required:
            - file
            - metadata
          type: object
          properties:
            file:
              type: string
              format: binary
            metadata:
              type: object
              properties:
                claimNumber:
                  type: string
                fileName:
                  type: string
                contentType:
                  type: string                    
  responses:
    201:
      description: OK
      content:
        text/plain:
          schema:
            type: string

When I use only simple types everything is ok:

/api/document:
put:
  tags:
    - document
  summary: upload
  operationId: upload
  requestBody:
    content:
      multipart/form-data:
        schema:
          required:
            - file
            - metadata
          type: object
          properties:
            file:
              type: string
              format: binary                
            claimNumber:
              type: string
            fileName:
              type: string
            contentType:
              type: string
  responses:
    201:
      description: OK
      content:
        text/plain:
          schema:
            type: string

Answer 1

You could try to be explicit about the content types of the fields (although the default for type: string format: binary should be application/octet-stream)

  requestBody:
    content:
      multipart/form-data:
        schema:
          required:
            - file
            - metadata
          type: object
          properties:
            file:
              type: string
              format: binary                
            claimNumber:
              type: string
            fileName:
              type: string
            contentType:
              type: string
        encoding:
          file:
            contentType: application/octet-stream
          claimNumber:
            contentType: text/plain
          fileName:
            contentType: text/plain
          contentType:
            contentType: text/plain