Encoding API: Handle null input string

LayoutTests/fast/encoding/api/basics.html

Index: LayoutTests/fast/encoding/api/basics.html
diff --git a/LayoutTests/fast/encoding/api/basics.html b/LayoutTests/fast/encoding/api/basics.html
index d95471265e0fc22add1a04c903ff2fa40e91ed1b..15b45a51edb6f226df45036735bf7c7c79d24bf5 100644
--- a/LayoutTests/fast/encoding/api/basics.html
+++ b/LayoutTests/fast/encoding/api/basics.html
@@ -23,6 +23,8 @@ test(function() {
     assert_equals((new TextEncoder).encoding, 'utf-8', 'default encoding is utf-8');
     assert_equals((new TextDecoder).encoding, 'utf-8', 'default encoding is utf-8');
 
+    assert_array_equals(new TextEncoder().encode(), [], 'input default should be empty string')
+
     function testEncodeDecodeSample(encoding, string, bytes) {
         var encoded = new TextEncoder(encoding).encode(string);
         assert_array_equals([].slice.call(encoded), bytes);