Wiki page comments unable to mention another user. Backend returns 500

WIth Wiki comments you are currently unable to mention another users. Backend returns 500

Internal server error: PG::NotNullViolation: ERROR:  null value in column \"namespace_id\" of relation \"wiki_page_meta_user_mentions\" violates not-null constraint\nDETAIL:  Failing row contains (2, 8, 1418, null, {1}, null, null).

~/.asdf/installs/ruby/3.2.4/lib/ruby/gems/3.2.0/gems/activerecord-7.0.8.6/lib/active_record/connection_adapters/postgresql_adapter.rb:768:in `exec_params' <--
~/.asdf/installs/ruby/3.2.4/lib/ruby/gems/3.2.0/gems/activerecord-7.0.8.6/lib/active_record/connection_adapters/postgresql_adapter.rb:768:in `block (2 levels) in exec_no_cache' <--
~/.asdf/installs/ruby/3.2.4/lib/ruby/gems/3.2.0/gems/activesupport-7.0.8.6/lib/active_support/concurrency/share_lock.rb:187:in `yield_shares' <--
~/.asdf/installs/ruby/3.2.4/lib/ruby/gems/3.2.0/gems/activesupport-7.0.8.6/lib/active_support/dependencies/interlock.rb:41:in `permit_concurrent_loads' <--
~/.asdf/installs/ruby/3.2.4/lib/ruby/gems/3.2.0/gems/activerecord-7.0.8.6/lib/active_record/connection_adapters/postgresql_adapter.rb:767:in `block in exec_no_cache' <--
~/.asdf/installs/ruby/3.2.4/lib/ruby/gems/3.2.0/gems/activesupport-7.0.8.6/lib/active_support/concurrency/load_interlock_aware_monitor.rb:25:in `handle_interrupt' <--
~/.asdf/installs/ruby/3.2.4/lib/ruby/gems/3.2.0/gems/activesupport-7.0.8.6/lib/active_support/concurrency/load_interlock_aware_monitor.rb:25:in `block in synchronize' <--
~/.asdf/installs/ruby/3.2.4/lib/ruby/gems/3.2.0/gems/activesupport-7.0.8.6/lib/active_support/concurrency/load_interlock_aware_monitor.rb:21:in `handle_interrupt' <--
~/.asdf/installs/ruby/3.2.4/lib/ruby/gems/3.2.0/gems/activesupport-7.0.8.6/lib/active_support/concurrency/load_interlock_aware_monitor.rb:21:in `synchronize' <--
~/.asdf/installs/ruby/3.2.4/lib/ruby/gems/3.2.0/gems/activerecord-7.0.8.6/lib/active_record/connection_adapters/abstract_adapter.rb:752:in `block in log' <--
~/.asdf/installs/ruby/3.2.4/lib/ruby/gems/3.2.0/gems/activesupport-7.0.8.6/lib/active_support/notifications/instrumenter.rb:24:in `instrument'

Example of error:

When trying to mention another user:

• It should create a todo in their profile.
• Send them an email. This is tracked in #508809.