Merge pull request #14773 from eric-chahin/null_relation_fix

Changed the NullRelation so that when count is called with #group it wil...
Conflicts:
	activerecord/CHANGELOG.md
	activerecord/lib/active_record/null_relation.rb

activerecord/CHANGELOG.md

@@ -1,3 +1,9 @@
+*   Fixed a problem where count used with a grouping was not returning a Hash.
+
+    Fixes #14721.
+
+    *Eric Chahin*
+
 *   Do not quote uuid default value on `change_column`.
 
     Fixes #14604.

activerecord/lib/active_record/null_relation.rb

@@ -43,15 +43,21 @@ def to_sql
     end
 
     def count(*)
-      0
+      calculate :count, nil
     end
 
     def sum(*)
       0
     end
 
-    def calculate(_operation, _column_name, _options = {})
-      nil
+    def calculate(operation, _column_name, _options = {})
+      # TODO: Remove _options argument as soon we remove support to
+      # activerecord-deprecated_finders.
+      if operation == :count
+        group_values.any? ? Hash.new : 0
+      else
+        nil
+      end
     end
 
     def exists?(_id = false)

activerecord/test/cases/relations_test.rb

@@ -14,6 +14,7 @@
 require 'models/engine'
 require 'models/tyre'
 require 'models/minivan'
+require 'models/aircraft'
 
 
 class RelationTest < ActiveRecord::TestCase
@@ -303,6 +304,16 @@ def test_null_relation_where_values_hash
     assert_equal({ 'salary' => 100_000 }, Developer.none.where(salary: 100_000).where_values_hash)
   end
 
+
+  def test_null_relation_count
+    ac = Aircraft.new
+    assert_equal Hash.new, ac.engines.group(:id).count
+    assert_equal        0, ac.engines.count
+    ac.save
+    assert_equal Hash.new, ac.engines.group(:id).count
+    assert_equal        0, ac.engines.count
+  end
+
   def test_joins_with_nil_argument
     assert_nothing_raised { DependentFirm.joins(nil).first }
   end