fixed: Unable to add threads with permission to edit CS but not in post group

docs/changelog/7.x.x.txt

@@ -4,6 +4,7 @@
  - fixed #11471: Errors in Calendar Event Edit template (Dale Trexel / U of MN Law School)
  - fixed #11475: Inherit permissions on imported package fails if asset already exists.
  - fixed #11476: Missing override in Page Layout shortcut
+ - fixed: Unable to add threads with permission to edit CS but not in post group
 
 7.9.0
  - added #11383: AJAX username checks at registration (Luke Robinson / Orchard Solutions)

lib/WebGUI/Asset/Post/Thread.pm

@@ -66,7 +66,7 @@ in the default asset, which better be a Collaboration System.
 sub canAdd {
     my $class   = shift;
     my $session = shift;
-    return $session->user->isInGroup($session->asset->get('canStartThreadGroupId'));
+    return $session->asset->isa('WebGUI::Asset::Wobject::Collaboration') && $session->asset->canStartThread;
 }
 
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