lockbox_repro.rb

require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'

  gem 'activerecord', require: 'active_record'
  gem 'sqlite3'
  gem 'lockbox', git: 'https://github.com/ankane/lockbox.git'
end

puts "Lockbox version: #{Lockbox::VERSION}"

Lockbox.master_key = '0'*64

ActiveRecord::Base.establish_connection adapter: 'sqlite3', database: ':memory:'

ActiveRecord::Schema.define do
  create_table :users do |t|
    t.text :email_ciphertext
    t.text :words_ciphertext #, null: false - cannot enforce not-null
  end
end

class User < ActiveRecord::Base
  has_encrypted :email
  has_encrypted :words, type: :hash
end

my_hash = { "word": 5 }
user = User.create!(email: 'test@example.com', words: nil)
pp user          # #<User id: 1, email: [FILTERED], words: nil>
pp user.words    # {}

user.update!(words: {}) 
pp user          # #<User id: 1, email: [FILTERED], words: nil>
pp user.words    # {} 

user.update!(words: {a: 2}) # error: Tried to load unspecified class: Symbol (Psych::DisallowedClass)
pp user
pp user.words