Fix Rails/HasManyOrHasOneDependent with nil

app/models/spree/adjustment.rb

@@ -36,7 +36,7 @@ module Spree
     # Deletion of metadata is handled in the database.
     # So we don't need the option `dependent: :destroy` as long as
     # AdjustmentMetadata has no destroy logic itself.
-    has_one :metadata, class_name: 'AdjustmentMetadata', dependent: :destroy
+    has_one :metadata, class_name: 'AdjustmentMetadata', dependent: nil
     has_many :adjustments, as: :adjustable, dependent: :destroy
 
     belongs_to :adjustable, polymorphic: true

app/models/spree/tax_rate.rb

@@ -21,7 +21,7 @@ module Spree
 
     belongs_to :zone, class_name: "Spree::Zone", inverse_of: :tax_rates
     belongs_to :tax_category, class_name: "Spree::TaxCategory", inverse_of: :tax_rates
-    has_many :adjustments, as: :originator, dependent: :destroy
+    has_many :adjustments, as: :originator, dependent: nil
 
     validates :amount, presence: true, numericality: true
     validates :tax_category, presence: true

app/models/spree/user.rb

@@ -14,7 +14,7 @@ module Spree
            encryptor: 'authlogic_sha512', reconfirmable: true,
            omniauth_providers: [:openid_connect]
 
-    has_many :orders
+    has_many :orders, dependent: nil
     belongs_to :ship_address, class_name: 'Spree::Address'
     belongs_to :bill_address, class_name: 'Spree::Address'
 

app/models/spree/variant.rb

@@ -33,8 +33,8 @@ module Spree
 
     delegate :name, :name=, :description, :description=, :meta_keywords, to: :product
 
-    has_many :inventory_units, inverse_of: :variant, dependent: :destroy
-    has_many :line_items, inverse_of: :variant, dependent: :destroy
+    has_many :inventory_units, inverse_of: :variant, dependent: nil
+    has_many :line_items, inverse_of: :variant, dependent: nil
 
     has_many :stock_items, dependent: :destroy, inverse_of: :variant
     has_many :stock_locations, through: :stock_items