Small fix in ExtendedURLField

oscar/forms/fields.py

@@ -21,6 +21,6 @@ class ExtendedURLField(fields.URLField):
     def to_python(self, value):
         # We need to avoid having 'http' inserted at the start of
         # every value
-        if value.startswith('/'):
+        if value and value.startswith('/'):
             return value
         return super(ExtendedURLField, self).to_python(value)