one more attempt

src/collective/ckeditor/browser/ckeditorsettings.py

@@ -11,7 +11,7 @@
 from zope.schema import ASCIILine
 from zope.schema import Bool
 from zope.schema import Choice
-from zope.schema import Bytes
+from zope.schema import Text
 from zope.schema import Tuple
 from zope.schema import List
 
@@ -104,7 +104,7 @@ class ICKEditorBaseSchema(Interface):
         ),
         required=False)
 
-    menuStyles = Bytes(
+    menuStyles = Text(
         title=_(u"Menu styles"),
         description=_(u"Build your own CKEditor menu styles Combo box. "
                       u"Take care with the javascript syntax. "

src/collective/ckeditor/pytests/test_upgrade.py

@@ -191,13 +191,13 @@ def test_upgrade_of_menuStyles(plone_instance):
     selected = soup.select("#form-widgets-value")
     assert len(selected) == 1
     field = selected[0]
-    assert field.name == "input"
+    assert field.name == "textarea"
     menuStyle = """
     { name : 'upgrade ascii Title'		, element : 'h2', styles : { 'color' : '#888' } },
     { name : 'upgrade unicode Title éè'		, element : 'h2', styles : { 'color' : '#888' } },
     """
     for line in menuStyle.splitlines():
-        assert line.strip() in field.value
+        assert line.strip() in field.text
 
 
 @pytest.mark.upgrade

src/collective/ckeditor/upgrades.py

@@ -334,21 +334,23 @@ def to_registry(context):
 IS_PYTHON2 = sys.version_info[0] == 2
 if IS_PYTHON2:
     text_type = unicode
+    binary_type = str
     string_none = "None"
 else:
     text_type = str
+    binary_type = bytes
     string_none = b"None"
 
 
 def safe_string(value):
     if value is None:
-        return ''
+        return binary_type()
     if isinstance(value, text_type):
         result = value.encode('utf8')
     else:
         result = value
     # workaround old settings screen that stored empty input as "None" string
     if result == string_none:
-        return ''
+        return binary_type()
     else:
         return result