Index: vm.c
===================================================================
--- vm.c	(revision 41200)
+++ vm.c	(working copy)
@@ -2181,7 +2181,7 @@
 static VALUE
 m_core_hash_merge_kwd(VALUE recv, VALUE hash, VALUE kw)
 {
-    kw = rb_convert_type(kw, T_HASH, "Hash", "to_hash");
+    kw = rb_Hash(kw);
     rb_hash_foreach(kw, kwmerge_i, hash);
     return hash;
 }
Index: test/ruby/test_keyword.rb
===================================================================
--- test/ruby/test_keyword.rb	(revision 41200)
+++ test/ruby/test_keyword.rb	(working copy)
@@ -8,6 +8,9 @@
 
   def test_f1
     assert_equal(["foo", 424242], f1)
+    assert_equal(["foo", 424242], f1(**nil))
+    assert_equal(["foo", 424242], f1(**[]))
+    assert_equal(["foo", 424242], f1(**{}))
     assert_equal(["bar", 424242], f1(str: "bar"))
     assert_equal(["foo", 111111], f1(num: 111111))
     assert_equal(["bar", 111111], f1(str: "bar", num: 111111))