Since #6873, Foreman isn't starting up on a clean installation with:

PGError: ERROR:  null value in column "user_id" violates not-null constraint
: INSERT INTO "cached_user_roles" ("created_at", "role_id", "updated_at", "user_id", "user_role_id") VALUES ($1, $2, $3, $4, $5) RETURNING "id" (ActiveRecord::StatementInvalid)
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/connection_adapters/postgresql_adapter.rb:1171:in `get_last_result'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/connection_adapters/postgresql_adapter.rb:1171:in `exec_cache'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/connection_adapters/postgresql_adapter.rb:665:in `block in exec_query'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/connection_adapters/abstract_adapter.rb:280:in `block in log'
  /opt/rh/ruby193/root/usr/share/gems/gems/activesupport-3.2.8/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/connection_adapters/abstract_adapter.rb:275:in `log'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/connection_adapters/postgresql_adapter.rb:663:in `exec_query'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/connection_adapters/abstract/database_statements.rb:63:in `exec_insert'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/connection_adapters/abstract/database_statements.rb:90:in `insert'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/connection_adapters/abstract/query_cache.rb:14:in `insert'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/relation.rb:66:in `insert'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/persistence.rb:366:in `create'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/timestamp.rb:57:in `create'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/callbacks.rb:268:in `block in create'
  /opt/rh/ruby193/root/usr/share/gems/gems/activesupport-3.2.8/lib/active_support/callbacks.rb:403:in `_run__4384089833700878333__create__735890728046573773__callbacks'
  /opt/rh/ruby193/root/usr/share/gems/gems/activesupport-3.2.8/lib/active_support/callbacks.rb:405:in `__run_callback'
  /opt/rh/ruby193/root/usr/share/gems/gems/activesupport-3.2.8/lib/active_support/callbacks.rb:385:in `_run_create_callbacks'
  /opt/rh/ruby193/root/usr/share/gems/gems/activesupport-3.2.8/lib/active_support/callbacks.rb:81:in `run_callbacks'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/callbacks.rb:268:in `create'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/persistence.rb:347:in `create_or_update'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/callbacks.rb:264:in `block in create_or_update'
  /opt/rh/ruby193/root/usr/share/gems/gems/activesupport-3.2.8/lib/active_support/callbacks.rb:436:in `_run__4384089833700878333__save__735890728046573773__callbacks'
  /opt/rh/ruby193/root/usr/share/gems/gems/activesupport-3.2.8/lib/active_support/callbacks.rb:405:in `__run_callback'
  /opt/rh/ruby193/root/usr/share/gems/gems/activesupport-3.2.8/lib/active_support/callbacks.rb:385:in `_run_save_callbacks'
  /opt/rh/ruby193/root/usr/share/gems/gems/activesupport-3.2.8/lib/active_support/callbacks.rb:81:in `run_callbacks'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/callbacks.rb:264:in `create_or_update'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/persistence.rb:104:in `save!'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/validations.rb:56:in `save!'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/attribute_methods/dirty.rb:33:in `save!'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/transactions.rb:246:in `block in save!'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/transactions.rb:295:in `block in with_transaction_returning_status'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/connection_adapters/abstract/database_statements.rb:192:in `transaction'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/transactions.rb:208:in `transaction'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/transactions.rb:293:in `with_transaction_returning_status'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/transactions.rb:246:in `save!'
  /usr/share/foreman/app/models/user_role.rb:58:in `each'
  /usr/share/foreman/app/models/user_role.rb:58:in `all?'
  /usr/share/foreman/app/models/user_role.rb:58:in `cache_user_roles!'
  /opt/rh/ruby193/root/usr/share/gems/gems/activesupport-3.2.8/lib/active_support/callbacks.rb:449:in `_run__4597219778037394767__save__735890728046573773__callbacks'
  /opt/rh/ruby193/root/usr/share/gems/gems/activesupport-3.2.8/lib/active_support/callbacks.rb:405:in `__run_callback'
  /opt/rh/ruby193/root/usr/share/gems/gems/activesupport-3.2.8/lib/active_support/callbacks.rb:385:in `_run_save_callbacks'
  /opt/rh/ruby193/root/usr/share/gems/gems/activesupport-3.2.8/lib/active_support/callbacks.rb:81:in `run_callbacks'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/callbacks.rb:264:in `create_or_update'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/persistence.rb:104:in `save!'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/validations.rb:56:in `save!'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/attribute_methods/dirty.rb:33:in `save!'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/transactions.rb:246:in `block in save!'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/transactions.rb:295:in `block in with_transaction_returning_status'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/connection_adapters/abstract/database_statements.rb:192:in `transaction'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/transactions.rb:208:in `transaction'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/transactions.rb:293:in `with_transaction_returning_status'
  /opt/rh/ruby193/root/usr/share/gems/gems/activerecord-3.2.8/lib/active_record/transactions.rb:246:in `save!'
  /usr/share/foreman/app/services/cache_manager.rb:9:in `map'
  /usr/share/foreman/app/services/cache_manager.rb:9:in `create_new_permission_cache'
  /usr/share/foreman/app/services/cache_manager.rb:19:in `recache!'
  /usr/share/foreman/config/initializers/fix_cache.rb:9:in `<top (required)>'
  /opt/rh/ruby193/root/usr/share/gems/gems/activesupport-3.2.8/lib/active_support/dependencies.rb:245:in `load'
  /opt/rh/ruby193/root/usr/share/gems/gems/activesupport-3.2.8/lib/active_support/dependencies.rb:245:in `block in load'
  /opt/rh/ruby193/root/usr/share/gems/gems/activesupport-3.2.8/lib/active_support/dependencies.rb:236:in `load_dependency'
  /opt/rh/ruby193/root/usr/share/gems/gems/activesupport-3.2.8/lib/active_support/dependencies.rb:245:in `load'
  /opt/rh/ruby193/root/usr/share/gems/gems/railties-3.2.8/lib/rails/engine.rb:588:in `block (2 levels) in <class:Engine>'
  /opt/rh/ruby193/root/usr/share/gems/gems/railties-3.2.8/lib/rails/engine.rb:587:in `each'
  /opt/rh/ruby193/root/usr/share/gems/gems/railties-3.2.8/lib/rails/engine.rb:587:in `block in <class:Engine>'
  /opt/rh/ruby193/root/usr/share/gems/gems/railties-3.2.8/lib/rails/initializable.rb:30:in `instance_exec'
  /opt/rh/ruby193/root/usr/share/gems/gems/railties-3.2.8/lib/rails/initializable.rb:30:in `run'
  /opt/rh/ruby193/root/usr/share/gems/gems/railties-3.2.8/lib/rails/initializable.rb:55:in `block in run_initializers'
  /opt/rh/ruby193/root/usr/share/gems/gems/railties-3.2.8/lib/rails/initializable.rb:54:in `each'
  /opt/rh/ruby193/root/usr/share/gems/gems/railties-3.2.8/lib/rails/initializable.rb:54:in `run_initializers'
  /opt/rh/ruby193/root/usr/share/gems/gems/railties-3.2.8/lib/rails/application.rb:136:in `initialize!'
  /opt/rh/ruby193/root/usr/share/gems/gems/railties-3.2.8/lib/rails/railtie/configurable.rb:30:in `method_missing'
  /usr/share/foreman/config/environment.rb:5:in `<top (required)>'
  /opt/rh/ruby193/root/usr/share/rubygems/rubygems/custom_require.rb:36:in `require'
  /opt/rh/ruby193/root/usr/share/rubygems/rubygems/custom_require.rb:36:in `require'
  config.ru:3:in `block in <main>'
  /opt/rh/ruby193/root/usr/share/gems/gems/rack-1.4.1/lib/rack/builder.rb:51:in `instance_eval'
  /opt/rh/ruby193/root/usr/share/gems/gems/rack-1.4.1/lib/rack/builder.rb:51:in `initialize'
  config.ru:1:in `new'
  config.ru:1:in `<main>'
  /usr/lib/ruby/gems/1.8/gems/passenger-4.0.18/helper-scripts/rack-preloader.rb:105:in `eval'
  /usr/lib/ruby/gems/1.8/gems/passenger-4.0.18/helper-scripts/rack-preloader.rb:105:in `preload_app'
  /usr/lib/ruby/gems/1.8/gems/passenger-4.0.18/helper-scripts/rack-preloader.rb:150:in `<module:App>'
  /usr/lib/ruby/gems/1.8/gems/passenger-4.0.18/helper-scripts/rack-preloader.rb:29:in `<module:PhusionPassenger>'
  /usr/lib/ruby/gems/1.8/gems/passenger-4.0.18/helper-scripts/rack-preloader.rb:28:in `<main>'

Looks similar to #4641, but could be unrelated.