I've installed ActiveAdmin v4.0.0.beta5, but fails on app execution with the error:

uninitialized constant #<Class:ActiveAdmin>::Importmap

That comes from lib/active_admin.rb.

Digging into that file, I've noticed that the requirement of 'importmap-rails' is optional:

begin
  require "importmap-rails"
rescue LoadError
  # importmap-rails is optional
end

But still fails when trying to load and instantiate Importmap.new.

Currently, we are using Rails 7.0, with Esbuild + Propshaft.