Always include the options :include_blank if the select has a require…

…d attribute

and display size 1 and not multiple attribute,  Fixes rails#5908

actionpack/lib/action_view/helpers/tags/base.rb

@@ -121,6 +121,7 @@ def sanitized_value(value)
         def select_content_tag(option_tags, options, html_options)
           html_options = html_options.stringify_keys
           add_default_name_and_id(html_options)
+          options[:include_blank] = true if option_required?(html_options)
           select = content_tag("select", add_options(option_tags, options, value(object)), html_options)
 
           if html_options["multiple"] && options.fetch(:include_hidden, true)
@@ -129,6 +130,10 @@ def select_content_tag(option_tags, options, html_options)
             select
           end
         end
+
+        def option_required?(html_options)
+          html_options["required"] && html_options["size"].to_i == 1 && !html_options["multiple"]
+        end
 
         def add_options(option_tags, options, value = nil)
           if options[:include_blank]

actionpack/test/template/form_options_helper_test.rb

@@ -633,7 +633,28 @@ def test_select_with_nil
       select("post", "category", [nil, "othervalue"])
     )
   end
+
+  def test_select_with_included_and_display_size_equals_to_one
+    assert_dom_equal(
+    "<select id=\"post_category\" name=\"post[category]\" required=\"required\" size=\"1\"><option value=\"\"></option>\n<option value=\"abe\">abe</option>\n<option value=\"mus\">mus</option>\n<option value=\"hest\">hest</option></select>",
+    select("post", "category", %w( abe mus hest),{}, :required => true, :size => 1)
+    )
+  end
+
+  def test_select_with_included_and_display_size_no_equals_to_one
+       assert_dom_equal(
+       "<select id=\"post_category\" name=\"post[category]\" required=\"required\" size=\"2\"><option value=\"abe\">abe</option>\n<option value=\"mus\">mus</option>\n<option value=\"hest\">hest</option></select>",
+       select("post", "category", %w( abe mus hest),{}, :required => true, :size => 2)
+       )
+  end
 
+  def test_select_with_included_and_multiple
+    assert_dom_equal(
+    "<input name=\"post[category][]\" type=\"hidden\" value=\"\"/><select id=\"post_category\" multiple=\"multiple\" name=\"post[category][]\" required=\"required\" size=\"1\"><option value=\"abe\">abe</option>\n<option value=\"mus\">mus</option>\n<option value=\"hest\">hest</option></select>",
+    select("post", "category", %w( abe mus hest), {}, :required => true, :size => 1, :multiple => true)
+    )
+  end
+
   def test_select_with_fixnum
     @post = Post.new
     @post.category = ""