Using OpenApi codegen for model generation, unable to make HashMap<String, HashMap<String, String>> (Spring, Java)

Within my .yaml file, I have this:

components:
  schemas:
    InformationObject:
      outsideInformationStructure:
        description: Outer structure to store all information.
        schema:
          $ref: "#/components/schemas/InsideInformationStructure"

    InsideInformationStructure:
      properties:
        firstField:
          type: string
          description: The first field that exists inside the data structure.
        secondField:
          type: string
          description: The second field that exists inside the data structure.

I want my data structure to look like HashMap<String, HashMap<String, String>>. Would this achieve that goal or am I missing something? I'm unsure of how to verify what I have.