Custom helper methods aren't rendered in 1.2.0

[seanlinsley]

As of version 1.2.0, this helper method no longer renders:

# _form.html.arb
active_admin_form_for [:admin, resource] do |f|
  error_banner(f)

  # ...
end

# app/helpers/admin/application_helper.rb
module Admin::ApplicationHelper
  def error_banner(form)
    # ...

    form.semantic_errors
  end
end

When inlining the code, however, it does render.

# _form.html.arb
active_admin_form_for [:admin, resource] do |f|
  f.semantic_errors

  # ...
end

This was likely caused by #64, and is related to #119.

It's not clear if the issue is specific to using Arbre templates (as opposed to inlined forms in app/admin), or using custom helper methods (as opposed to Rails helper methods).