Use nil? instead of blank? to check dynamic finder result

It's safe to use `nil?` instead of `blank?` because it's impossible to get an array on finder with bang;
`all_by` finder matches against regex without bang: `when /^find_(all_|last_)?by_([_a-zA-Z]\w*)$/`.

Fixes #7238

2 files changed, 11 insertions, 0 deletions

diff --git a/activerecord/test/cases/finder_test.rb b/activerecord/test/cases/finder_test.rb
index 5d72e35c60..e50a334958 100644
--- a/activerecord/test/cases/finder_test.rb
+++ b/activerecord/test/cases/finder_test.rb
@@ -652,6 +652,11 @@ class FinderTest < ActiveRecord::TestCase
     assert_raise(ActiveRecord::RecordNotFound) { Topic.find_by_title!("The First Topic!") }
   end
 
+  def test_find_by_one_attribute_bang_with_blank_defined
+    blank_topic = BlankTopic.create(:title => "The Blank One")
+    assert_equal blank_topic, BlankTopic.find_by_title!("The Blank One")
+  end
+
   def test_find_by_one_attribute_with_order_option
     assert_equal accounts(:signals37), Account.find_by_credit_limit(50, :order => 'id')
     assert_equal accounts(:rails_core_account), Account.find_by_credit_limit(50, :order => 'id DESC')
diff --git a/activerecord/test/models/topic.rb b/activerecord/test/models/topic.rb
index 1a1a18166a..5166fefe81 100644
--- a/activerecord/test/models/topic.rb
+++ b/activerecord/test/models/topic.rb
@@ -112,6 +112,12 @@ class ImportantTopic < Topic
   serialize :important, Hash
 end
 
+class BlankTopic < Topic
+  def blank?
+    true
+  end
+end
+
 module Web
   class Topic < ActiveRecord::Base
     has_many :replies, :dependent => :destroy, :foreign_key => "parent_id", :class_name => 'Web::Reply'