Merge branch 'issue_14671' into 'master'

Fix cancel button on issuables

Fixes #14671

See merge request !3417

app/views/shared/issuable/_form.html.haml

@@ -127,7 +127,7 @@
       for this project.
 
   - if issuable.new_record?
-    = link_to 'Cancel', polymorphic_path([@project.namespace, @project, issuable.class]), class: 'btn btn-cancel'
+    = link_to 'Cancel', polymorphic_path([@project.namespace.becomes(Namespace), @project, issuable.class]), class: 'btn btn-cancel'
   - else
     .pull-right
       - if current_user.can?(:"destroy_#{issuable.to_ability_name}", @project)