Fix specs

app/models/merge_request.rb

@@ -183,7 +183,7 @@ class MergeRequest < ActiveRecord::Base
   def diff_base_commit
     if merge_request_diff
       merge_request_diff.base_commit
-    else
+    elsif source_sha
       self.target_project.merge_base_commit(self.source_sha, self.target_branch)
     end
   end
@@ -489,7 +489,7 @@ class MergeRequest < ActiveRecord::Base
   end
   def source_sha
-    last_commit.sha
+    last_commit.try(:sha)
   end
   def fetch_ref

app/models/project.rb

@@ -349,7 +349,8 @@ class Project < ActiveRecord::Base
   end
   def merge_base_commit(first_commit_id, second_commit_id)
-    repository.commit(repository.merge_base(first_commit_id, second_commit_id))
+    sha = repository.merge_base(first_commit_id, second_commit_id)
+    repository.commit(sha) if sha
   end
   def saved?

app/models/repository.rb

@@ -589,6 +589,8 @@ class Repository
   def merge_base(first_commit_id, second_commit_id)
     rugged.merge_base(first_commit_id, second_commit_id)
+  rescue Rugged::ReferenceError
+    nil
   end
   def is_ancestor?(ancestor_id, descendant_id)

spec/models/build_spec.rb

 require 'spec_helper'
 describe Ci::Build, models: true do
-  let(:project) { FactoryGirl.create :empty_project }
+  let(:project) { FactoryGirl.create :project }
   let(:commit) { FactoryGirl.create :ci_commit, project: project }
   let(:build) { FactoryGirl.create :ci_build, commit: commit }