fix UrlGenerationError: No route matches

app/models/pull_request.rb

@@ -180,6 +180,7 @@ class PullRequest < ActiveRecord::Base
   end
 
   def clone
+    return if from_project.nil?
     git = Grit::Git.new(path)
     if new_record? || !git.exist?
       #~ FileUtils.mkdir_p(path)

app/views/projects/pull_requests/_pull_diff.html.haml

@@ -3,7 +3,8 @@
   %a{name: "diff-#{pull_diff_counter}"}
   .top
     .l= h(pull_diff.renamed_file ? "#{pull_diff.a_path.rtruncate 60}=>#{pull_diff.b_path.rtruncate 60}" : pull_diff.b_path.rtruncate(120))
-    .r= link_to "view file @ #{short_hash_id(commit_id)}", blob_path(@pull.from_project, commit_id, pull_diff.b_path)
+    - if @pull.from_project.present?
+      .r= link_to "view file @ #{short_hash_id(commit_id)}", blob_path(@pull.from_project, commit_id, pull_diff.b_path)
     .clear
   -if pull_diff.diff.present? && !(@pull.repo.tree(commit_id) / pull_diff.b_path).binary?
     .diff_data=render_diff(pull_diff, diff_counter: pull_diff_counter, comments: @comments)