Merge pull request #14773 from eric-chahin/null_relation_fix

Changed the NullRelation so that when count is called with #group it wil...

activerecord/CHANGELOG.md

+*   Fixed a problem where count used with a grouping was not returning a Hash.
+
+    Fixes #14721.
+
+    *Eric Chahin*
+
 *   `sanitize_sql_like` helper method to escape a string for safe use in a SQL
     LIKE statement.
 

activerecord/lib/active_record/null_relation.rb

@@ -43,7 +43,7 @@ def to_sql
     end
 
     def count(*)
-      0
+      calculate :count, nil
     end
 
     def sum(*)
@@ -54,7 +54,7 @@ def calculate(operation, _column_name, _options = {})
       # TODO: Remove _options argument as soon we remove support to
       # activerecord-deprecated_finders.
       if operation == :count
-        0
+        group_values.any? ? Hash.new : 0
       else
         nil
       end

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
@@ -365,6 +366,16 @@ 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