What steps will reproduce the problem?
1. create a model with a blob property
2. create a new object of this type
3. with this object : myobj.to_xml()

What is the expected output? What do you see instead?
expected : display the xml

i see an error :
Traceback (most recent call last):
  File "C:\Program
Files\Google\google_appengine\google\appengine\ext\webapp\__init__.py",
line 501, in __call__
    handler.post(*groups)
  File "C:\Outils\eclipse\workspace\nopix\src\main.py", line 101, in post
    logging.info(imgt.to_xml())
  File "C:\Program
Files\Google\google_appengine\google\appengine\ext\db\__init__.py", line
718, in to_xml
    return entity.ToXml()
  File "C:\Program
Files\Google\google_appengine\google\appengine\api\datastore.py", line 403,
in ToXml
    xml += '\n  ' + '\n  '.join(self._PropertiesToXml(properties))
  File "C:\Program
Files\Google\google_appengine\google\appengine\api\datastore.py", line 433,
in _PropertiesToXml
    escaped_values = self._XmlEscapeValues(propname)
  File "C:\Program
Files\Google\google_appengine\google\appengine\api\datastore.py", line 464,
in _XmlEscapeValues
    xml.append(saxutils.escape(unicode(val)))
UnicodeDecodeError: 'ascii' codec can't decode byte 0xff in position 0:
ordinal not in range(128)


What version of the product are you using? On what operating system?
GAE 1.10 / Win XP sp2

Please provide any additional information below.

class Image(db.Model):
   pic = db.BlobProperty()

mypic = Image()
xml = mypic.to_xml() --> CRASH