Merge branch 'fix-ci-charts-error-500' into 'master'

Fix Error 500 in CI charts by gracefully handling commits with no durations

## What does this MR do?

In the CI charts, this MR reports the duration of a commit to 0 if it is `nil`.

## Are there points in the code the reviewer needs to double check?

Should we omit this commit from the chart or set it to some other value?

## Why was this MR needed?

We were getting an Error 500 here: https://gitlab.com/gitlab-org/gitlab-ce/graphs/master/ci

## What are the relevant issue numbers?

#17730 


See merge request !4245

CHANGELOG

@@ -5,6 +5,7 @@ v 8.8.2
   - Fix access to Pipelines by Anonymous user. !4233
 v 8.8.2 (unreleased)
   - Fix Error 500 when accessing application settings due to nil disabled OAuth sign-in sources
+  - Fix Error 500 in CI charts by gracefully handling commits with no durations
 
 v 8.8.1
   - Add documentation for the "Health Check" feature

lib/ci/charts.rb

@@ -64,7 +64,8 @@ module Ci
 
         commits.each do |commit|
           @labels << commit.short_sha
-          @build_times << (commit.duration / 60)
+          duration = commit.duration || 0
+          @build_times << (duration / 60)
         end
       end
     end

spec/lib/ci/charts_spec.rb

@@ -12,5 +12,12 @@ describe Ci::Charts, lib: true do
       chart = Ci::Charts::BuildTime.new(@commit.project)
       expect(chart.build_times).to eq([2])
     end
+
+    it 'should handle nil build times' do
+      create(:ci_commit, duration: nil, project: @commit.project)
+
+      chart = Ci::Charts::BuildTime.new(@commit.project)
+      expect(chart.build_times).to eq([2, 0])
+    end
   end
 end