Modified find project method to return nil if project not found

app/views/search/results/_blob.html.haml

 - project = find_project_for_result_blob(blob)
+- return unless project
+
 - file_name, blob = parse_search_result(blob)
 - blob_link = project_blob_path(project, tree_join(blob.ref, file_name))
 

ee/app/helpers/ee/search_helper.rb

@@ -11,7 +11,7 @@ module EE
 
     override :find_project_for_result_blob
     def find_project_for_result_blob(result)
-      super || ::Project.find(result['_parent'])
+      super || ::Project.find_by(id: result['_parent'])
     end
 
     override :parse_search_result

ee/changelogs/unreleased/ccr-5300-elasticsearch_index.yml

+---
+title: Don't show search results for projects that have been deleted when using elastic search
+merge_request: 6830
+author:
+type: fixed

ee/spec/features/search/elastic/global_search_spec.rb

@@ -36,6 +36,8 @@ describe 'Global elastic search' do
   end
 
   describe 'I search through the blobs' do
+    let(:project_2) { create(:project, :repository, :wiki_repo) }
+
     before do
       project.repository.index_blobs
 
@@ -54,6 +56,28 @@ describe 'Global elastic search' do
 
       expect(page).to have_selector("span.line[lang='javascript']")
     end
+
+    it 'Ignores nonexistent projects from stale index' do
+      stub_ee_application_setting(elasticsearch_search: true, elasticsearch_indexing: true)
+
+      project_2.repository.create_file(
+        user,
+        'thing.txt',
+        ' function application.js ',
+        message: 'supercalifragilisticexpialidocious',
+        branch_name: 'master')
+
+      project_2.repository.index_blobs
+      Gitlab::Elastic::Helper.refresh_index
+      project_2.destroy
+
+      visit dashboard_projects_path
+
+      fill_in "search", with: "application.js"
+      click_button "Go"
+
+      expect(page).not_to have_content 'supercalifragilisticexpialidocious'
+    end
   end
 
   describe 'I search through the wiki blobs' do

ee/spec/helpers/search_helper_spec.rb

@@ -2,6 +2,8 @@ require 'spec_helper'
 
 describe SearchHelper do
   describe '#parse_search_result_from_elastic' do
+    let(:user) { create(:user) }
+
     before do
       stub_ee_application_setting(elasticsearch_search: true, elasticsearch_indexing: true)
       Gitlab::Elastic::Helper.create_empty_index
@@ -32,5 +34,28 @@ describe SearchHelper do
       expect(parsed_result.startline).to eq(2)
       expect(parsed_result.data).to include("Popen")
     end
+
+    it 'does not return project that does not exist' do
+      Gitlab::Elastic::Helper.create_empty_index
+
+      @project_2 = create :project, :repository
+
+      @project_2.repository.create_file(
+        user,
+        'thing.txt',
+        ' function application.js ',
+        message: 'Find me',
+        branch_name: 'master')
+
+      @project_2.repository.index_blobs
+      Gitlab::Elastic::Helper.refresh_index
+      @project_2.destroy
+
+      blob = { _parent: @project_2.id }
+
+      result = find_project_for_result_blob(blob)
+
+      expect(result).to be(nil)
+    end
   end
 end