--- a/src/pyams_utils/text.py	Tue Sep 25 11:28:03 2018 +0200
+++ b/src/pyams_utils/text.py	Thu Sep 27 14:37:47 2018 +0200
@@ -12,8 +12,6 @@
 
 __docformat__ = 'restructuredtext'
 
-
-# import standard library
 import html
 
 import docutils.core
@@ -21,9 +19,7 @@
 from zope.interface import Interface
 from zope.schema.vocabulary import SimpleTerm, SimpleVocabulary
 
-# import packages
 from pyams_utils.adapter import ContextRequestAdapter, ContextRequestViewAdapter, adapter_config
-# import interfaces
 from pyams_utils.interfaces.tales import ITALESExtension
 from pyams_utils.interfaces.text import IHTMLRenderer
 from pyams_utils.request import check_request
@@ -127,6 +123,9 @@
         return renderer.render()
 
 
+empty_marker = object()
+
+
 @adapter_config(name='html', context=(Interface, Interface, Interface), provides=ITALESExtension)
 class HTMLTalesExtension(ContextRequestViewAdapter):
     """*extension:html* TALES expression
@@ -137,9 +136,11 @@
     converted to string using the :py:func:`str` function.
     """
 
-    def render(self, context=None, renderer='text'):
-        if context is None:
+    def render(self, context=empty_marker, renderer='text'):
+        if context is empty_marker:
             context = self.context
+        if not context:
+            return ''
         registry = self.request.registry
         adapter = registry.queryMultiAdapter((context, self.request, self.view), IHTMLRenderer)
         if adapter is None: