Add support for nil scope values (such as deleted_at), with unit test

lib/stringex/acts_as_url/adapter/base.rb

@@ -64,8 +64,10 @@ def add_new_record_url_owner_conditions
 
         def add_scoped_url_owner_conditions
           [settings.scope_for_url].flatten.compact.each do |scope|
-            @url_owner_conditions.first << " and #{scope} = ?"
-            @url_owner_conditions << instance.send(scope)
+            scope_val = instance.send(scope)
+            sql_operator = scope_val.nil? ? "IS" : "="
+            @url_owner_conditions.first << " AND #{scope} #{sql_operator} ?"
+            @url_owner_conditions << scope_val
           end
         end
 

test/unit/acts_as_url_integration_test.rb

@@ -177,6 +177,22 @@ def test_should_only_create_unique_urls_for_multiple_scopes_if_both_attributes_a
     assert_not_equal @doc.url, @other_doc.url
   end
 
+  def test_should_create_uniuque_urls_for_nil_scope_values
+    Document.class_eval do
+      acts_as_url :title, scope: %i[other, another]
+    end
+
+    @doc = Document.create(title: "Soft Deleted Document", 
+                           other: "scope key",
+                           another: nil)
+
+    @other_doc = Document.create(title: "Soft Deleted Document", 
+                                 other: "scope key",
+                                 another: nil)
+
+    assert_not_equal @doc.url, @other_doc.url
+  end
+
   def test_should_allow_setting_url_attribute
     Document.class_eval do
       # Manually undefining the url method on Document which, in a real class not reused for tests,