Stoping using Relation#merge in default_scoped

Relation#merge checks if the argument is an array and the only possible
returns of build_default_scope is nil or a Relation.

Doing this we can raise an ArgumentError when Relation#merge receive a
nil value.

1 files changed, 7 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/scoping/named.rb b/activerecord/lib/active_record/scoping/named.rb
index 35420e6551..a083deafe1 100644
--- a/activerecord/lib/active_record/scoping/named.rb
+++ b/activerecord/lib/active_record/scoping/named.rb
@@ -30,7 +30,13 @@ module ActiveRecord
         end
 
         def default_scoped # :nodoc:
-          relation.merge(build_default_scope)
+          scope = build_default_scope
+
+          if scope
+            relation.spawn.merge!(scope)
+          else
+            relation
+          end
         end
 
         # Collects attributes from scopes that should be applied when creating