Don't attempt to look up an avatar in repo if repo directory does not exist

Closes #14580

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.7.0 (unreleased)
+  - Don't attempt to look up an avatar in repo if repo directory does not exist (Stan hu)
   - Preserve time notes/comments have been updated at when moving issue
   - Make HTTP(s) label consistent on clone bar (Stan Hu)
   - Fix avatar stretching by providing a cropping feature

app/models/repository.rb

@@ -877,6 +877,8 @@ class Repository
   end
 
   def avatar
+    return nil unless exists?
+
     @avatar ||= cache.fetch(:avatar) do
       AVATAR_FILES.find do |file|
         blob_at_branch('master', file)

spec/models/project_spec.rb

@@ -422,6 +422,12 @@ describe Project, models: true do
 
       it { should eq "http://localhost#{avatar_path}" }
     end
+
+    context 'when git repo is empty' do
+      let(:project) { create(:empty_project) }
+
+      it { should eq nil }
+    end
   end
 
   describe :ci_commit do

spec/models/repository_spec.rb

@@ -725,6 +725,12 @@ describe Repository, models: true do
   end
 
   describe '#avatar' do
+    it 'returns nil if repo does not exist' do
+      expect(repository).to receive(:exists?).and_return(false)
+
+      expect(repository.avatar).to eq(nil)
+    end
+
     it 'returns the first avatar file found in the repository' do
       expect(repository).to receive(:blob_at_branch).
         with('master', 'logo.png').