Fix an oversight in r83294. unquote() should reject bytes. Issue #9301.

Lib/test/test_urllib.py

@@ -557,6 +557,7 @@ class UnquotingTests(unittest.TestCase):
                          "%s" % result)
         self.assertRaises((TypeError, AttributeError), urllib.parse.unquote, None)
         self.assertRaises((TypeError, AttributeError), urllib.parse.unquote, ())
+        self.assertRaises((TypeError, AttributeError), urllib.parse.unquote, b'')
 
     def test_unquoting_badpercent(self):
         # Test unquoting on bad percent-escapes

Lib/urllib/parse.py

@@ -338,7 +338,7 @@ def unquote(string, encoding='utf-8', errors='replace'):
 
     unquote('abc%20def') -> 'abc def'.
     """
-    if string in (b'', ''):
+    if string == '':
         return string
     res = string.split('%')
     if len(res) == 1: