Properly check if there's error on input.

Aslo if there's no error class setup on wrapper then there's
no need to check for errors.

lib/simple_form/wrappers/many.rb

@@ -68,7 +68,11 @@ def html_options(options)
 
       def html_classes(input, options)
         css = @defaults[:class].dup
-        css << @defaults[:error_class].dup { input.has_errors? }
+
+        if @defaults[:error_class] && input.has_errors?
+          css << @defaults[:error_class]
+        end
+
         css.compact
       end
     end

test/form_builder/wrapper_test.rb

@@ -382,4 +382,11 @@ class WrapperTest < ActionView::TestCase
       assert_select 'section.custom_wrapper div.custom_error'
     end
   end
+
+  test 'inline wrapper has no error class when there is no error' do
+    swap_wrapper :default, custom_wrapper_with_error_class do
+      with_form_for @user, :email
+      assert_no_select 'section.custom_wrapper div.custom_error'
+    end
+  end
 end