class ViewModel::Registry

def clear_removed_classes!

their constant
For Rails hot code loading: ditch any classes that are not longer present at 
def clear_removed_classes!
  @lock.synchronize do
    resolve_deferred_classes
    @viewmodel_classes_by_name.delete_if do |_name, klass|
      !Kernel.const_defined?(klass.name)
    end
  end
end