ClassCastException when walking over input types that have GraphQLTypeReferences

[edudar-chwy]

Describe the bug

java.lang.ClassCastException: class graphql.schema.GraphQLTypeReference cannot be cast to class graphql.schema.GraphQLUnmodifiedType (graphql.schema.GraphQLTypeReference and graphql.schema.GraphQLUnmodifiedType are in unnamed module of loader 'app')
  at graphql.schema.GraphQLTypeUtil.unwrapAll(GraphQLTypeUtil.java:194)
  at graphql.validation.util.DirectivesAndTypeWalker.walkInputType(DirectivesAndTypeWalker.java:23)
  at graphql.validation.util.DirectivesAndTypeWalker.isSuitable(DirectivesAndTypeWalker.java:19)

To Reproduce
I have an enum type that is used as non-null input

enum SlotType {
    AVAILABLE, UNAVAILABLE
}

type Employee {
  schedule(type: SlotType!): [Slot!]!
}

DirectivesAndTypeWalker uses GraphQLTypeUtil.unwrapAll(inputType) since #34 but unwrapAll specifically says that it does not support GraphQLTypeReference:

Unwraps all layers of the type or just returns the type again if it's not a wrapped type NOTE: This method does not support GraphQLTypeReference as input and will lead to a ClassCastException

and SlotType turns out to be one:

type = {GraphQLNonNull@17904} "SlotType!"
 originalWrappedType = {GraphQLTypeReference@17955} "GraphQLTypeReference{name='SlotType'}"
  name = "SlotType"
 replacedWrappedType = null

[dondonz]

Hello, to help me understand the issue can you please provide a minimal test case as a pull request or reproduction of the bug in a repo? Thanks