fix: resolving wrong reference

[VisualBean]

About the PR

When a reference is resolved, that doesnt map to the correct type, for instance;

asyncapi: 2.3.0
info:
  title: test
  version: 1.0.0
channels:
  workspace:
    publish:
      message:
        $ref: '#/components/securitySchemes/saslScram'
components:
  securitySchemes:
    saslScram:
      type: scramSha256
      description: Provide your username and password for SASL/SCRAM authentication

mapping a message to a securityScheme. No error will be present in the diagnostics object.
The message will simply be null.

This PR adds a quick and dirty exception to reference resolution when casting to T ends with being null.