project_from_ref returns nil when reference doesn't exist.

lib/gitlab/markdown/cross_project_reference.rb

@@ -16,15 +16,12 @@ module Gitlab
       #
       # Returns a Project, or nil if the reference can't be accessed
       def project_from_ref(ref)
-        if ref && other = Project.find_with_namespace(ref)
-          if user_can_reference_project?(other)
-            other
-          else
-            nil
-          end
-        else
-          context[:project]
-        end
+        return context[:project] unless ref
+
+        other = Project.find_with_namespace(ref)
+        return nil unless other && user_can_reference_project?(other)
+        
+        other
       end
 
       def user_can_reference_project?(project, user = context[:current_user])

spec/lib/gitlab/markdown/cross_project_reference_spec.rb

@@ -13,9 +13,15 @@ module Gitlab::Markdown
     include described_class
 
     describe '#project_from_ref' do
-      context 'when referenced project does not exist' do
+      context 'when no project was referenced' do
         it 'returns the project from context' do
-          expect(project_from_ref('invalid/reference')).to eq context[:project]
+          expect(project_from_ref(nil)).to eq context[:project]
+        end
+      end
+
+      context 'when referenced project does not exist' do
+        it 'returns nil' do
+          expect(project_from_ref('invalid/reference')).to be_nil
         end
       end