Use safe_constantize instead

Plus, use `nil?` to be idiomatic.

Author: jnraine

lib/polymorphic_integer_type/extensions.rb

@@ -84,14 +84,9 @@ def remove_type_and_establish_mapping(name, options, scope)
       end
 
       def retrieve_polymorphic_type_mapping(polymorphic_type:, class_name:)
-        return if polymorphic_type == nil
-
-        belongs_to_class = begin
-          class_name.constantize
-        rescue NameError
-          # Class not found
-        end
+        return if polymorphic_type.nil?
 
+        belongs_to_class = class_name.safe_constantize
         method_name = "#{polymorphic_type}_type_mapping"
 
         if belongs_to_class && belongs_to_class.respond_to?(method_name)