Adds a specific ArgumentError when passing nil to dom_id. Which can h…

…appen if you do something like pass a non-existent ivar dom_id(@something_non_existant)

Before this would raise: `NoMethodError: undefined method `to_key' for nil:NilClass`
After it raises `ArumentError: dom_id must be passed a record_or_class as the first parameter, you passed 'nil'`

actionview/lib/action_view/record_identifier.rb

@@ -91,6 +91,8 @@ def dom_class(record_or_class, prefix = nil)
     #   dom_id(Post.find(45), :edit) # => "edit_post_45"
     #   dom_id(Post, :custom)        # => "custom_post"
     def dom_id(record_or_class, prefix = nil)
+      raise ArgumentError, "dom_id must be passed a record_or_class as the first argument, you passed #{record_or_class.inspect}" unless record_or_class
+
       record_id = record_key_for_dom_id(record_or_class) unless record_or_class.is_a?(Class)
       if record_id
         "#{dom_class(record_or_class, prefix)}#{JOIN}#{record_id}"

actionview/test/template/record_identifier_test.rb

@@ -83,6 +83,12 @@ def test_dom_id_with_prefix
     assert_equal "edit_airplane_1", dom_id(@record, :edit)
   end
 
+  def test_dom_id_raises_useful_error_when_passed_nil
+    assert_raises ArgumentError do
+      ActionView::RecordIdentifier.dom_id(nil)
+    end
+  end
+
   def test_dom_class
     assert_equal "airplane", dom_class(@record)
   end