NoMethodError: undefined method `login_name' for nil:NilClass

[komagata]

View details in Rollbar: https://app.rollbar.com/a/komagata/fix/item/Bootcamp/1660

NoMethodError: undefined method `login_name' for nil:NilClass
  File "/app/app/models/concerns/mentioner.rb", line 71, in target_of_comment
  File "/app/app/models/concerns/mentioner.rb", line 21, in where_mention
  File "/app/app/notifiers/activity_notifier.rb", line 196, in mentioned
  File "/usr/local/bundle/gems/abstract_notifier-0.3.2/lib/abstract_notifier/base.rb", line 39, in public_send
  File "/usr/local/bundle/gems/abstract_notifier-0.3.2/lib/abstract_notifier/base.rb", line 39, in method_missing
  File "/usr/local/bundle/gems/abstract_notifier-0.3.2/lib/active_delivery/lines/notifier.rb", line 32, in public_send
  File "/usr/local/bundle/gems/abstract_notifier-0.3.2/lib/active_delivery/lines/notifier.rb", line 32, in notify_later
  File "/usr/local/bundle/gems/active_delivery-0.4.4/lib/active_delivery/lines/base.rb", line 37, in notify
  File "/usr/local/bundle/gems/active_delivery-0.4.4/lib/active_delivery/base.rb", line 121, in notify_line
  File "/usr/local/bundle/gems/active_delivery-0.4.4/lib/active_delivery/callbacks.rb", line 49, in block in notify_line
  File "/usr/local/bundle/gems/activesupport-6.1.4.7/lib/active_support/callbacks.rb", line 98, in run_callbacks
  File "/usr/local/bundle/gems/active_delivery-0.4.4/lib/active_delivery/callbacks.rb", line 49, in notify_line
  File "/usr/local/bundle/gems/active_delivery-0.4.4/lib/active_delivery/base.rb", line 116, in block in do_notify
  File "/usr/local/bundle/gems/active_delivery-0.4.4/lib/active_delivery/base.rb", line 112, in each
  File "/usr/local/bundle/gems/active_delivery-0.4.4/lib/active_delivery/base.rb", line 112, in do_notify
  File "/usr/local/bundle/gems/active_delivery-0.4.4/lib/active_delivery/callbacks.rb", line 45, in block in do_notify
  File "/usr/local/bundle/gems/activesupport-6.1.4.7/lib/active_support/callbacks.rb", line 98, in run_callbacks
  File "/usr/local/bundle/gems/active_delivery-0.4.4/lib/active_delivery/callbacks.rb", line 45, in do_notify
  File "/usr/local/bundle/gems/active_delivery-0.4.4/lib/active_delivery/base.rb", line 100, in notify
  File "/app/app/models/concerns/mentioner.rb", line 48, in block in notify_mentions
  File "/usr/local/bundle/gems/activerecord-6.1.4.7/lib/active_record/relation/delegation.rb", line 88, in each
  File "/usr/local/bundle/gems/activerecord-6.1.4.7/lib/active_record/relation/delegation.rb", line 88, in each
  File "/app/app/models/concerns/mentioner.rb", line 47, in notify_mentions
  File "/app/app/models/concerns/mentioner.rb", line 41, in notify_users_found_by_mentions
  File "/app/app/models/concerns/mentioner.rb", line 7, in after_save_mention
  File "/usr/local/bundle/gems/mentionable-0.3.0/lib/mentionable.rb", line 20, in public_send
  File "/usr/local/bundle/gems/mentionable-0.3.0/lib/mentionable.rb", line 20, in block in mentionable_as
  File "/usr/local/bundle/gems/activesupport-6.1.4.7/lib/active_support/callbacks.rb", line 427, in instance_exec
  File "/usr/local/bundle/gems/activesupport-6.1.4.7/lib/active_support/callbacks.rb", line 427, in block in make_lambda
  File "/usr/local/bundle/gems/activesupport-6.1.4.7/lib/active_support/callbacks.rb", line 270, in block in simple
  File "/usr/local/bundle/gems/activesupport-6.1.4.7/lib/active_support/callbacks.rb", line 516, in block in invoke_after
  File "/usr/local/bundle/gems/activesupport-6.1.4.7/lib/active_support/callbacks.rb", line 516, in each
  File "/usr/local/bundle/gems/activesupport-6.1.4.7/lib/active_support/callbacks.rb", line 516, in invoke_after
  File "/usr/local/bundle/gems/activesupport-6.1.4.7/lib/active_support/callbacks.rb", line 107, in run_callbacks
  File "/usr/local/bundle/gems/activesupport-6.1.4.7/lib/active_support/callbacks.rb", line 824, in _run_commit_callbacks
  File "/usr/local/bundle/gems/activerecord-6.1.4.7/lib/active_record/transactions.rb", line 321, in committed!
  File "/usr/local/bundle/gems/activerecord-6.1.4.7/lib/active_record/connection_adapters/abstract/transaction.rb", line 155, in commit_records
  File "/usr/local/bundle/gems/activerecord-6.1.4.7/lib/active_record/connection_adapters/abstract/transaction.rb", line 304, in block in commit_transaction
  File "/usr/local/bundle/gems/activesupport-6.1.4.7/lib/active_support/concurrency/load_interlock_aware_monitor.rb", line 26, in block (2 levels) in synchronize
  File "/usr/local/bundle/gems/activesupport-6.1.4.7/lib/active_support/concurrency/load_interlock_aware_monitor.rb", line 25, in handle_interrupt
  File "/usr/local/bundle/gems/activesupport-6.1.4.7/lib/active_support/concurrency/load_interlock_aware_monitor.rb", line 25, in block in synchronize
  File "/usr/local/bundle/gems/activesupport-6.1.4.7/lib/active_support/concurrency/load_interlock_aware_monitor.rb", line 21, in handle_interrupt
  File "/usr/local/bundle/gems/activesupport-6.1.4.7/lib/active_support/concurrency/load_interlock_aware_monitor.rb", line 21, in synchronize
  File "/usr/local/bundle/gems/activerecord-6.1.4.7/lib/active_record/connection_adapters/abstract/transaction.rb", line 294, in commit_transaction
  File "/usr/local/bundle/gems/activerecord-6.1.4.7/lib/active_record/connection_adapters/abstract/transaction.rb", line 351, in block in within_new_transaction
  File "/usr/local/bundle/gems/activesupport-6.1.4.7/lib/active_support/concurrency/load_interlock_aware_monitor.rb", line 26, in block (2 levels) in synchronize
  File "/usr/local/bundle/gems/activesupport-6.1.4.7/lib/active_support/concurrency/load_interlock_aware_monitor.rb", line 25, in handle_interrupt
  File "/usr/local/bundle/gems/activesupport-6.1.4.7/lib/active_support/concurrency/load_interlock_aware_monitor.rb", line 25, in block in synchronize
  File "/usr/local/bundle/gems/activesupport-6.1.4.7/lib/active_support/concurrency/load_interlock_aware_monitor.rb", line 21, in handle_interrupt
  File "/usr/local/bundle/gems/activesupport-6.1.4.7/lib/active_support/concurrency/load_interlock_aware_monitor.rb", line 21, in synchronize
  File "/usr/local/bundle/gems/activerecord-6.1.4.7/lib/active_record/connection_adapters/abstract/transaction.rb", line 317, in within_new_transaction
  File "/usr/local/bundle/gems/activerecord-6.1.4.7/lib/active_record/connection_adapters/abstract/database_statements.rb", line 320, in transaction
  File "/usr/local/bundle/gems/activerecord-6.1.4.7/lib/active_record/transactions.rb", line 350, in with_transaction_returning_status
  File "/usr/local/bundle/gems/activerecord-6.1.4.7/lib/active_record/transactions.rb", line 294, in destroy
  File "/app/app/controllers/admin/users_controller.rb", line 39, in destroy
  File "/usr/local/bundle/gems/actionpack-6.1.4.7/lib/action_controller/metal/basic_implicit_render.rb", line 6, in send_action
  File "/usr/local/bundle/gems/actionpack-6.1.4.7/lib/abstract_controller/base.rb", line 228, in process_action
  File