Allow accessing preferences on models that do not have any set

core/app/models/spree/base.rb

@@ -5,6 +5,10 @@ class Spree::Base < ActiveRecord::Base
   include Spree::Core::Permalinks
   include Spree::RansackableAttributes
 
+  def preferences
+    read_attribute(:preferences) || self.class.preferences_coder_class.new
+  end
+
   def initialize_preference_defaults
     if has_attribute?(:preferences)
       self.preferences = default_preferences.merge(preferences)
@@ -16,11 +20,15 @@ def initialize_preference_defaults
   def self.preference(*args)
     # after_initialize can be called multiple times with the same symbol, it
     # will only be called once on initialization.
-    serialize :preferences, Hash
+    serialize :preferences, preferences_coder_class
     after_initialize :initialize_preference_defaults
     super
   end
 
+  def self.preferences_coder_class
+    Hash
+  end
+
   self.abstract_class = true
 
   # Provides a scope that should be included any time products

core/spec/models/spree/stock/estimator_spec.rb

@@ -96,6 +96,24 @@ module Stock
         context "general shipping methods" do
           before { Spree::ShippingMethod.all.each(&:destroy) }
 
+          context 'with a custom shipping calculator with no preference' do
+            class Spree::Calculator::Shipping::NoPreferences < Spree::ShippingCalculator
+              def compute_package(_package)
+                # no op
+              end
+            end
+
+            let!(:shipping_methods) do
+              [
+                create(:shipping_method, calculator: Spree::Calculator::Shipping::NoPreferences.new)
+              ]
+            end
+
+            it 'does not raise an error' do
+              expect { subject.shipping_rates(package) }.not_to raise_error
+            end
+          end
+
           context 'with two shipping methods of different cost' do
             let!(:shipping_methods) do
               [