Remove the upgrade task and point to additional steps from the update generator

core/lib/generators/solidus/update/update_generator.rb

@@ -57,6 +57,22 @@ def create_new_defaults_initializer
                File.join(options[:initializer_directory], "#{options[:initializer_basename]}.rb")
     end
 
+    def print_message
+      say <<~MSG
+
+        ***********************************************************************
+
+        Other tasks may be needed to update to the new Solidus version. Please,
+        check https://github.com/solidusio/solidus/blob/v#{options[:to]}/CHANGELOG.md
+        for details.
+
+        Thanks for using Solidus!
+
+        ***********************************************************************
+
+      MSG
+    end
+
     private
 
     def core_changes_template(from, to)

core/lib/tasks/solidus/delete_prices_with_nil_amount.rake

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+namespace :solidus do
+  desc "Delete Spree::Price records which amount field is NULL"
+  task delete_prices_with_nil_amount: :environment do
+    Spree::Price.where(amount: nil).delete_all
+  end
+end

core/spec/lib/tasks/migrations/delete_prices_with_nil_amount_spec.rb → core/spec/lib/tasks/solidus/delete_prices_with_nil_amount_spec.rb

@@ -2,14 +2,14 @@
 
 require 'rails_helper'
 
-path = Spree::Core::Engine.root.join('lib/tasks/migrations/delete_prices_with_nil_amount.rake')
+path = Spree::Core::Engine.root.join('lib/tasks/solidus/delete_prices_with_nil_amount.rake')
 
-RSpec.describe 'solidus:migrations:delete_prices_with_nil_amount' do
-  describe 'up' do
+RSpec.describe 'solidus' do
+  describe 'delete_prices_with_nil_amount' do
     include_context(
       'rake',
       task_path: path,
-      task_name: 'solidus:migrations:delete_prices_with_nil_amount:up'
+      task_name: 'solidus:delete_prices_with_nil_amount'
     )
 
     it 'removes all prices which amount column is NULL' do