Fix the instance of template object in closure

Author: chechaoyang

lib/active_admin_import/dsl.rb

@@ -33,13 +33,12 @@ def active_admin_import options = {}, &block
           headers_rewrites: {}
       }
       options = default_options.deep_merge(options)
-      options[:template_object] = ActiveAdminImport::Model.new if options[:template_object].blank?
-      params_key = ActiveModel::Naming.param_key(options[:template_object])
+      params_key = ActiveModel::Naming.param_key(options[:template_object] || ActiveAdminImport::Model.new)
 
       collection_action :import, method: :get do
         authorize!(ActiveAdminImport::Auth::IMPORT, active_admin_config.resource_class)
 
-        @active_admin_import_model = options[:template_object]
+        @active_admin_import_model = options[:template_object] || ActiveAdminImport::Model.new
         render template: options[:template]
       end
 
@@ -52,7 +51,7 @@ def active_admin_import options = {}, &block
       collection_action :do_import, method: :post do
         authorize!(ActiveAdminImport::Auth::IMPORT, active_admin_config.resource_class)
 
-        @active_admin_import_model = options[:template_object]
+        @active_admin_import_model = options[:template_object] || ActiveAdminImport::Model.new
         @active_admin_import_model.assign_attributes(params[params_key].try(:deep_symbolize_keys) || {})
         #go back to form
         return render template: options[:template] unless @active_admin_import_model.valid?