only yield to finder block if something is found

activerecord/lib/active_record/relation/finder_methods.rb

@@ -217,7 +217,7 @@ def find_by_attributes(match, attributes, *args)
       if match.bang? && result.blank?
         raise RecordNotFound, "Couldn't find #{@klass.name} with #{conditions.to_a.collect {|p| p.join(' = ')}.join(', ')}"
       else
-        yield(result) if block_given?
+        yield(result) if block_given? && result
         result
       end
     end

activerecord/test/cases/base_test.rb

@@ -175,6 +175,16 @@ def test_table_exists
     assert Topic.table_exists?
   end
 
+  def test_finder_block
+    t = Topic.first
+    found = nil
+    Topic.find_by_id(t.id) { |f| found = f }
+    assert_equal t, found
+
+    bad_id = Topic.maximum(:id) + 1
+    Topic.find_by_id(bad_id) { |f| raise }
+  end
+
   def test_preserving_date_objects
     if current_adapter?(:SybaseAdapter)
       # Sybase ctlib does not (yet?) support the date type; use datetime instead.