Don't return the same object when using find with an empty array

When you pass an empty array to find we know we shoudl return an empty
array but it is surprising that we are returning the original empty
array instead of a new one.

activerecord/lib/active_record/relation/finder_methods.rb

@@ -416,7 +416,7 @@ module ActiveRecord
         raise UnknownPrimaryKey.new(@klass) if primary_key.nil?
 
         expects_array = ids.first.kind_of?(Array)
-        return ids.first if expects_array && ids.first.empty?
+        return [] if expects_array && ids.first.empty?
 
         ids = ids.flatten.compact.uniq
 

activerecord/test/cases/finder_test.rb

@@ -371,7 +371,10 @@ class FinderTest < ActiveRecord::TestCase
   end
 
   def test_find_an_empty_array
-    assert_equal [], Topic.find([])
+    empty_array = []
+    result = Topic.find(empty_array)
+    assert_equal [], result
+    assert_not_same empty_array, result
   end
 
   def test_find_doesnt_have_implicit_ordering