✅ Adds a guard clause to fix failing tests

This commit adds a guard clause to the `SortTitle` model to fix failing
tests due to a nil value being assigned to `@title` on initialization.

Ref:
- scientist-softserv/adventist_knapsack#185

app/models/sort_title.rb

@@ -6,6 +6,8 @@ def initialize(title)
   end
 
   def alphabetical
+    return if @title.blank?
+
     title = @title.downcase
     title = title.gsub(/^an(?:[[:space:]])/, '')
                  .gsub(/^a(?:[[:space:]])/, '')