Allow returning nil for `default_scope`

activerecord/lib/active_record/scoping/default.rb

@@ -100,7 +100,7 @@ module ActiveRecord
             self.default_scopes += [scope]
           end
 
-          def build_default_scope(base_rel = nil)
+          def build_default_scope(relation = relation())
             return if abstract_class?
 
             if default_scope_override.nil?
@@ -111,15 +111,14 @@ module ActiveRecord
               # The user has defined their own default scope method, so call that
               evaluate_default_scope do
                 if scope = default_scope
-                  (base_rel ||= relation).merge!(scope)
+                  relation.merge!(scope)
                 end
               end
             elsif default_scopes.any?
-              base_rel ||= relation
               evaluate_default_scope do
-                default_scopes.inject(base_rel) do |default_scope, scope|
+                default_scopes.inject(relation) do |default_scope, scope|
                   scope = scope.respond_to?(:to_proc) ? scope : scope.method(:call)
-                  default_scope.merge!(base_rel.instance_exec(&scope))
+                  default_scope.instance_exec(&scope) || default_scope
                 end
               end
             end

activerecord/test/models/developer.rb

@@ -207,6 +207,7 @@ end
 class MultiplePoorDeveloperCalledJamis < ActiveRecord::Base
   self.table_name = "developers"
 
+  default_scope { }
   default_scope -> { where(name: "Jamis") }
   default_scope -> { where(salary: 50000) }
 end