Admin "searches" view returns HTTP 500 when there are no searches with hits

[bencomp]

In our test environment I tried a single search that had no results. I then went to the admin dashboard, clicked the "Searches" tab and was presented with an internal server error, instead of the overview I had seen when there were no searches at all.

The logs show:

I, [2024-10-24T12:50:41.041167 #295]  INFO -- : Started GET "/admin/searches" for <IP> at 2024-10-24 12:50:41 +0000
I, [2024-10-24T12:50:41.043500 #295]  INFO -- : Processing by AdminController#searches as HTML
I, [2024-10-24T12:50:41.066908 #295]  INFO -- : Completed 500  in 23ms (ActiveRecord: 4.2ms | Allocations: 7768)
F, [2024-10-24T12:50:41.069929 #295] FATAL -- :   
NoMethodError (undefined method `round' for nil:NilClass):
  
app/controllers/admin_controller.rb:304:in `searches'
app/controllers/application_controller.rb:78:in `switch_locale'
app/controllers/application_controller.rb:33:in `check_deleted_articles'

fromthepage/app/controllers/admin_controller.rb

Lines 299 to 310 in 8408e08

	this_week = SearchAttempt.where('created_at > ?', 1.week.ago)
	unless this_week.empty?
	by_visit = this_week.joins(:visit).group('visits.id')
	@find_a_project_searches_per_day = (this_week.where(search_type: 'findaproject').count / 7.0).round(2)
	@collection_work_searches_per_day = (this_week.where.not(search_type: 'findaproject').count / 7.0).round(2)
	@find_a_project_average_hits = this_week.where(search_type: 'findaproject').average(:hits).round(2)
	@collection_work_average_hits = this_week.where.not(search_type: 'findaproject').average(:hits).round(2)
	@clickthrough_rate = ((this_week.where('clicks > 0').count.to_f / this_week.count) * 100).round(1)
	@clickthrough_rate_visit = ((by_visit.sum(:clicks).values.count{|c|c>0}.to_f / by_visit.length) * 100).round(1)
	@contribution_rate = ((this_week.where('contributions > 0').count.to_f / this_week.count) * 100).round(1)
	@contribution_rate_visit = ((by_visit.sum(:contributions).values.count{|c|c>0}.to_f / by_visit.length) * 100).round(1)
	end

According to https://api.rubyonrails.org/classes/ActiveRecord/Calculations.html#method-i-average, the .average method returns nil when there are no rows. In my case, I hadn't searched for a project, so it breaks on line 304. I guess that if I had only searched for a project but not for or within a collection, it would break on line 305.