Make List#last more similar to Array#last

At the expense of some complexity, this handles properly nil or false
being passed as an argument by using a specific value to encode that no
arguments were passed to the method.

It still raises a NoMethodError to_int instead of a TypeError, but the
additional complexity is not worth the runtime cost IMO.

Author: etiennebarrie

lib/kredis/types/list.rb

@@ -25,8 +25,11 @@ def clear
     del
   end
 
-  def last(n = nil)
-    if n
+  NO_ARGUMENT = Object.new
+  private_constant :NO_ARGUMENT
+
+  def last(n = NO_ARGUMENT)
+    if n != NO_ARGUMENT
       n = n.to_int
       if n == 0
         []

test/types/list_test.rb

@@ -52,6 +52,9 @@ class ListTest < ActiveSupport::TestCase
     assert_equal %w[ 2 3 ], @list.last(2.0)
     assert_equal [], @list.last(0)
     assert_raises(ArgumentError) { @list.last(-2) }
+    assert_raises { @list.last(nil) }
+    assert_raises { @list.last(false) }
+    assert_raises { @list.last(BasicObject.new) }
   end
 
   test "typed as datetime" do