diff --git a/spec/instance_template/attributes_spec.cr b/spec/instance_template/attributes_spec.cr
index a1584ca..24f4a9d 100644
--- a/spec/instance_template/attributes_spec.cr
+++ b/spec/instance_template/attributes_spec.cr
@@ -8,7 +8,7 @@ module ToHtml::InstanceTemplate::AttributesSpec
     ToHtml.instance_template do
       div MyCssClass, MyOtherCssClass, {"class", "so-unique"}, more_css_classes do
         span(SPECIAL_CSS_CLASSES) { "Blah" }
-        img SPECIAL_CSS_CLASSES, more_css_classes
+        img SPECIAL_CSS_CLASSES, more_css_classes, {"class", nil}
         div MyStimulusController do
           p({"class", "so-special"}) do
             "Some content"
@@ -17,10 +17,10 @@ module ToHtml::InstanceTemplate::AttributesSpec
       end
 
       fieldset do
-        label for: SomeId.to_s do
+        label for: SomeId do
           "Options"
         end
-        select_tag id: SomeId.to_s, name: "myselect" do
+        select_tag id: SomeId, name: "myselect" do
           option(value: "", selected: false) { "-" }
           ["one", "two", "three"].each do |val|
             option(value: val, selected: val == DEFAULT_VALUE) { val }
diff --git a/src/attribute_hash.cr b/src/attribute_hash.cr
index d279ce7..9a1b288 100644
--- a/src/attribute_hash.cr
+++ b/src/attribute_hash.cr
@@ -17,9 +17,9 @@ module ToHtml
 
     def []=(key, value)
       if attributes.has_key?(key)
-        attributes[key] += " #{value}"
+        attributes[key] += " #{value}" if value
       else
-        attributes[key] = value
+        attributes[key] = value.to_s
       end
     end