DiscriminatorNode access on undefined property

Describe the bug

With version 4.2.0 OAS discriminator was changed and now results in "This page crashed": TypeError: undefined is not an object (evaluating 'subProperties[discriminator.propertyName]') errors.

Rolling back to 4.1.0 fixes the issue but shows "circular(InnerClassTypeA)".

Your Environment

• Version used: 4.2.0

Context

The relevant part of redacted OAS looks like this:

# ...
components:
  schemas:
    OuterClass:
      type: object
      properties:
        _TYPE:
          type: string
          enum:
            - type1
            - type2
        sharedProperty:
          type: string
     discriminator:
       propertyName: _TYPE
       mapping:
         type1: "#components/schemas/OuterClassType1"
         type2: "#components/schemas/OuterClassType2"
    OuterClassType1:
      allOf:
        - $ref: "#components/schemas/OuterClass"
        - type: object
          properties:
            # property named the same but different concrete schema per discriminated property
            innerClass:
              $ref: "#components/schemas/InnerClassTypeA"
    OuterClassType2:
      allOf:
        - $ref: "#components/schemas/OuterClass"
        - type: object
          properties:
            # property named the same but different concrete schema per discriminated property
            innerClass:
              $ref: "#components/schemas/InnerClassTypeB"
    # never used directly but only "inherited" from with allOf
    InnerClass:
      type: object
      properties:
        _TYPE:
          type: string
          enum:
            - typeA
            - typeB
        sharedProperty:
          type: string
     discriminator:
       propertyName: _TYPE
       mapping:
         type1: "#components/schemas/InnerClassTypeA"
         type2: "#components/schemas/InnerClassTypeB"
    InnerClassTypeA:
      allOf:
        - $ref: "#components/schemas/InnerClass"
        - type: object
          properties:
            specificFieldA:
              type: string
    InnerClassTypeB:
      allOf:
        - $ref: "#components/schemas/InnerClass"
        - type: object
          properties:
            specificFieldB:
              type: string

Reproduce the crash using the redacted OAS schema in the issue and compare the discriminator behavior between versions 4.1.0 and 4.2.0. No files or tests are named, so first trace the schema rendering path that accesses subProperties; done means the supplied nested allOf/discriminator case renders without the undefined-property error.