change model arg default to false; raise if model arg is nil

Author: cjilbert504

actionview/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   Raise `ArgumentError` when `nil` is passed as `model:` argument value to the `form_with` method.
+
+    *Collin Jilbert*
+
 *   Alias `field_set_tag` helper to `fieldset_tag` to match `<fieldset>` element
 
     *Sean Doyle*

actionview/lib/action_view/helpers/form_helper.rb

@@ -437,7 +437,7 @@ def form_for(record, options = {}, &block)
 
         case record
         when String, Symbol
-          model       = nil
+          model       = false
           object_name = record
         else
           model       = record
@@ -753,7 +753,9 @@ def apply_form_for_options!(object, options) # :nodoc:
       #   def labelled_form_with(**options, &block)
       #     form_with(**options.merge(builder: LabellingFormBuilder), &block)
       #   end
-      def form_with(model: nil, scope: nil, url: nil, format: nil, **options, &block)
+      def form_with(model: false, scope: nil, url: nil, format: nil, **options, &block)
+        raise ArgumentError, "The :model argument cannot be nil" if model.nil?
+
         options = { allow_method_names_outside_object: true, skip_default_ids: !form_with_generates_ids }.merge!(options)
 
         if model

actionview/test/template/form_helper/form_with_test.rb

@@ -339,6 +339,14 @@ def url_for(object)
     super
   end
 
+  def test_form_with_when_given_nil_model_argument
+    error = assert_raises(ArgumentError) do
+      form_with(model: nil) do
+      end
+    end
+    assert_equal "The :model argument cannot be nil", error.message
+  end
+
   def test_form_with
     form_with(model: @post, id: "create-post") do |f|
       concat f.label(:title) { "The Title" }