`list_users_by_email` returns `nil` when successful

[francois]

Checklist

• I have looked into the Readme and Examples, and have not found a suitable solution or answer.
• I have looked into the API documentation and have not found a suitable solution or answer.
• I have searched the issues and have not found a suitable solution or answer.
• I have searched the Auth0 Community forums and have not found a suitable solution or answer.
• I agree to the terms within the Auth0 Code of Conduct.

Description

#list_users_by_email returns nil in the success case.

The root cause seems to be this line:

https://github.com/auth0/ruby-auth0/blame/5ae44e930b3272f9aff0e1a4fc082342afdf233b/lib/auth0/users/client.rb#L178

Notice this line does return if code.between?(200, 299).

Reproduction

#!/usr/bin/env ruby
require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'
  gem 'auth0', '= 6.0.0'
end

# v6 mistakenly does not require this file as part of the gem's default
# load, so it must be required explicitly.
require 'auth0/version'
puts "Auth0::VERSION = #{Auth0::VERSION}"

domain = ENV.fetch('AUTH0_DOMAIN')
client_id = ENV.fetch('AUTH0_CLIENT_ID')
client_secret = ENV.fetch('AUTH0_CLIENT_SECRET')
email = ENV.fetch('AUTH0_TEST_EMAIL')

auth0_client = Auth0::Client.new(
  client_id: client_id,
  client_secret: client_secret,
  domain: domain
)

list = auth0_client.users.list_users_by_email(email: email)

if list.nil?
  puts 'nil list'
else
  puts "#{list.size} items"
end

#!/usr/bin/env ruby
require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'
  gem 'auth0', '= 5.20.0'
end

require 'auth0/version'
puts "Auth0::VERSION = #{Auth0::VERSION}"

domain = ENV.fetch('AUTH0_DOMAIN')
client_id = ENV.fetch('AUTH0_CLIENT_ID')
client_secret = ENV.fetch('AUTH0_CLIENT_SECRET')
email = ENV.fetch('AUTH0_TEST_EMAIL')

auth0_client = Auth0::Client.new(
  client_id: client_id,
  client_secret: client_secret,
  domain: domain
)

list = auth0_client.users_by_email(email)

if list.nil?
  puts 'nil list'
else
  puts "#{list.size} items"
end

Results:

$ AUTH0_DOMAIN=aloft-toolkit-prod.us.auth0.com AUTH0_CLIENT_ID=... AUTH0_CLIENT_SECRET=... AUTH0_TEST_EMAIL=engineering@appraisify.com ruby repro5.rb
Auth0::VERSION = 5.20.0
1 items

$ AUTH0_DOMAIN=aloft-toolkit-prod.us.auth0.com AUTH0_CLIENT_ID=... AUTH0_CLIENT_SECRET=... AUTH0_TEST_EMAIL=engineering@appraisify.com ruby repro6.rb
Auth0::VERSION = 6.0.0
nil list

$ ruby --version
ruby 4.0.6 (2026-07-14 revision 03b6d3f889) +PRISM [arm64-darwin24]

Additional context

This is running as part of a Rails application

ruby-auth0 version

6.0.0

Ruby version

4.0.6