diff --git a/markdownx/widgets.py b/markdownx/widgets.py
index 907f953..872b2c4 100755
--- a/markdownx/widgets.py
+++ b/markdownx/widgets.py
@@ -9,7 +9,9 @@ from .settings import MARKDOWNX_EDITOR_RESIZABLE
 class MarkdownxWidget(forms.Textarea):
 
     def render(self, name, value, attrs=None):
-        if 'class' in attrs.keys():
+        if attrs is None:
+            attrs = {}
+        elif 'class' in attrs:
             attrs['class'] += ' markdownx-editor'
         else:
             attrs.update({'class':'markdownx-editor'})