Additional spec and fix for edge case

I am still investigating if this case is something considered normal in
our data model.
But in out gitlabhq tarball we have such cases.
I am also checking why this was not failing on master.
Probably we are not passing keys with empty arrays into RelationFactory
at all?

lib/gitlab/import_export/relation_factory.rb

@@ -277,7 +277,7 @@ module Gitlab
       end
 
       def setup_pipeline
-        @relation_hash.fetch('stages').each do |stage|
+        @relation_hash.fetch('stages', []).each do |stage|
           stage.statuses.each do |status|
             status.pipeline = imported_object
           end

spec/fixtures/lib/gitlab/import_export/complex/project.json

@@ -6680,6 +6680,25 @@
           ]
         }
       ]
+    },
+    {
+      "id": 41,
+      "project_id": 5,
+      "ref": "master",
+      "sha": "2ea1f3dec713d940208fb5ce4a38765ecb5d3f73",
+      "before_sha": null,
+      "push_data": null,
+      "created_at": "2016-03-22T15:20:35.763Z",
+      "updated_at": "2016-03-22T15:20:35.763Z",
+      "tag": null,
+      "yaml_errors": null,
+      "committed_at": null,
+      "status": "failed",
+      "started_at": null,
+      "finished_at": null,
+      "duration": null,
+      "stages": [
+      ]
     }
   ],
   "triggers": [

spec/lib/gitlab/import_export/project_tree_restorer_spec.rb

@@ -260,9 +260,9 @@ describe Gitlab::ImportExport::ProjectTreeRestorer do
         end
 
         it 'has the correct number of pipelines and statuses' do
-          expect(@project.ci_pipelines.size).to eq(5)
+          expect(@project.ci_pipelines.size).to eq(6)
 
-          @project.ci_pipelines.zip([2, 2, 2, 2, 2])
+          @project.ci_pipelines.zip([0, 2, 2, 2, 2, 2])
             .each do |(pipeline, expected_status_size)|
             expect(pipeline.statuses.size).to eq(expected_status_size)
           end
@@ -271,7 +271,7 @@ describe Gitlab::ImportExport::ProjectTreeRestorer do
 
       context 'when restoring hierarchy of pipeline, stages and jobs' do
         it 'restores pipelines' do
-          expect(Ci::Pipeline.all.count).to be 5
+          expect(Ci::Pipeline.all.count).to be 6
         end
 
         it 'restores pipeline stages' do