NoMethodError: undefined method `key' for nil:NilClass

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NoMethodError: undefined method `key' for nil:NilClass
  File "/var/www/sites/blacklight/lib/blacklight/catalog.rb", line 82, in facet
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/action_controller/metal/implicit_render.rb", line 4, in send_action
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/abstract_controller/base.rb", line 198, in process_action
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/action_controller/metal/rendering.rb", line 10, in process_action
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/abstract_controller/callbacks.rb", line 20, in block in process_action
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/activesupport-4.2.11.3/lib/active_support/callbacks.rb", line 117, in call
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/activesupport-4.2.11.3/lib/active_support/callbacks.rb", line 555, in block (2 levels) in compile
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/activesupport-4.2.11.3/lib/active_support/callbacks.rb", line 505, in call
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/activesupport-4.2.11.3/lib/active_support/callbacks.rb", line 92, in __run_callbacks__
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/activesupport-4.2.11.3/lib/active_support/callbacks.rb", line 778, in _run_process_action_callbacks
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/activesupport-4.2.11.3/lib/active_support/callbacks.rb", line 81, in run_callbacks
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/abstract_controller/callbacks.rb", line 19, in process_action
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/action_controller/metal/rescue.rb", line 29, in process_action
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/action_controller/metal/instrumentation.rb", line 32, in block in process_action
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/activesupport-4.2.11.3/lib/active_support/notifications.rb", line 164, in block in instrument
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/activesupport-4.2.11.3/lib/active_support/notifications/instrumenter.rb", line 20, in instrument
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/activesupport-4.2.11.3/lib/active_support/notifications.rb", line 164, in instrument
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/action_controller/metal/instrumentation.rb", line 30, in process_action
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/action_controller/metal/params_wrapper.rb", line 250, in process_action
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/activerecord-4.2.11.3/lib/active_record/railties/controller_runtime.rb", line 18, in process_action
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/abstract_controller/base.rb", line 137, in process
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionview-4.2.11.3/lib/action_view/rendering.rb", line 30, in process
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/action_controller/metal.rb", line 196, in dispatch
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/action_controller/metal/rack_delegation.rb", line 13, in dispatch
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/action_controller/metal.rb", line 237, in block in action
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/action_dispatch/routing/route_set.rb", line 74, in dispatch
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/action_dispatch/routing/route_set.rb", line 43, in serve
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/action_dispatch/journey/router.rb", line 43, in block in serve
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/action_dispatch/journey/router.rb", line 30, in each
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/action_dispatch/journey/router.rb", line 30, in serve
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/action_dispatch/routing/route_set.rb", line 817, in call
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/warden-1.2.7/lib/warden/manager.rb", line 36, in block in call
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/warden-1.2.7/lib/warden/manager.rb", line 35, in catch
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/warden-1.2.7/lib/warden/manager.rb", line 35, in call
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/rack-1.6.13/lib/rack/etag.rb", line 24, in call
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/rack-1.6.13/lib/rack/conditionalget.rb", line 25, in call
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/rack-1.6.13/lib/rack/head.rb", line 13, in call
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/action_dispatch/middleware/params_parser.rb", line 27, in call
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/action_dispatch/middleware/flash.rb", line 260, in call
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/rack-1.6.13/lib/rack/session/abstract/id.rb", line 252, in context
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/rack-1.6.13/lib/rack/session/abstract/id.rb", line 247, in call
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/action_dispatch/middleware/cookies.rb", line 560, in call
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/activerecord-4.2.11.3/lib/active_record/query_cache.rb", line 36, in call
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/activerecord-4.2.11.3/lib/active_record/connection_adapters/abstract/connection_pool.rb", line 653, in call
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/action_dispatch/middleware/callbacks.rb", line 29, in block in call
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/activesupport-4.2.11.3/lib/active_support/callbacks.rb", line 88, in __run_callbacks__
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/activesupport-4.2.11.3/lib/active_support/callbacks.rb", line 778, in _run_call_callbacks
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/activesupport-4.2.11.3/lib/active_support/callbacks.rb", line 81, in run_callbacks
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actionpack-4.2.11.3/lib/action_dispatch/middleware/callbacks.rb", line 27, in call
  File "/var/www/sites/blacklight/vendor/ruby/2.5.0/gems/actio