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

activerecord/CHANGELOG.md

@@ -1,5 +1,10 @@
 ## Rails 3.2.10 (unreleased)
 
+*   Use `nil?` instead of `blank?` to check whether dynamic finder with a bang
+    should raise RecordNotFound. Fixes #7238.
+
+    *Nikita Afanasenko*
+
 *   Use query cache/uncache when using ENV["DATABASE_URL"].
     Fixes #6951. [Backport #8074]
 

activerecord/lib/active_record/relation/finder_methods.rb

@@ -263,7 +263,7 @@ module ActiveRecord
       conditions = Hash[attributes.map {|a| [a, args[attributes.index(a)]]}]
       result = where(conditions).send(match.finder)
 
-      if match.bang? && result.blank?
+      if match.bang? && result.nil?
         raise RecordNotFound, "Couldn't find #{@klass.name} with #{conditions.to_a.collect {|p| p.join(' = ')}.join(', ')}"
       else
         yield(result) if block_given?

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')

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'