swagger-v2-converter incorrectly converts 2.0 schemas that do not have the 'type' keyword

2.0 schemas without the type keyword are incorrectly converted to a ObjectSchema. For example, consider the following OAS 2.0 document:

swagger: '2.0'
info:
  title: AnyType test
  version: '1.0.0'
paths: {}
definitions:
  Foo:
    type: object
    properties:
      p1:
        type: object
      p2:
        description: test

Property p1 is an object, which is represented as a ObjectSchema. Property p2 does not have the type keyword specified, hence its value can be anything. It should be modeled an instance of the Schema class with the type property set to the null value. Currently it is modeled as an instance of ObjectSchema and the type property is set to object.

Start at the swagger-v2-converter entry point and reproduce the OAS 2.0 document from the issue, focusing on conversion of the Foo definition and its p1 and p2 properties. Done means p1 remains an ObjectSchema while p2 is represented by Schema with a null type.