Update schema.rb

app/jobs/migration/set_default_value_for_contact_name_job.rb

@@ -0,0 +1,11 @@
+class Migration::SetDefaultValueForContactNameJob < ApplicationJob
+  queue_as :scheduled_jobs
+
+  def perform(account)
+    account.contacts.each do |contact|
+      # rubocop:disable Rails/SkipsModelValidations
+      contact.update_columns(name: '') if contact.name.blank?
+      # rubocop:enable Rails/SkipsModelValidations
+    end
+  end
+end

db/migrate/20230512040636_set_default_name_to_existing_contacts.rb

@@ -0,0 +1,10 @@
+class SetDefaultNameToExistingContacts < ActiveRecord::Migration[7.0]
+  def change
+    ::Account.find_in_batches do |account_batch|
+      Rails.logger.info "Migrated till #{account_batch.first.id}\n"
+      account_batch.each do |account|
+        Migration::SetDefaultValueForContactNameJob.perform_later(account)
+      end
+    end
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.0].define(version: 2023_05_10_113208) do
+ActiveRecord::Schema[7.0].define(version: 2023_05_12_040636) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_stat_statements"
   enable_extension "pg_trgm"