export_content raises AttributeError: get with Plone 2.8.7

[rpijlman]

Same issue as #48

Commit 192fed7 in collective.jsonify 1.5 causes an exception in export_content with Zope 2.8.7-final, python 2.3.5, linux3:

Traceback (most recent call last):
File "/home/software/zope/2.8/lib/python/ZPublisher/Publish.py", line 114, in publish
request, bind=1)
File "/home/software/zope/2.8/lib/python/ZPublisher/mapply.py", line 88, in mapply
if debug is not None: return debug(object,args,context)
File "/home/software/zope/2.8/lib/python/ZPublisher/Publish.py", line 40, in call_object
result=apply(object,args) # Type s to step into published object.
File "/home/software/zope/2.8/lib/python/Products/ExternalMethod/ExternalMethod.py", line 225, in call
try: return f(*args, **kw)
File "/home/zope/productie/Extensions/json_methods.py", line 16, in export_content
extra_skip_classname=[], # optional list of classnames to skip
File "/home/software/python/2.3.5/lib/python2.3/site-packages/collective.jsonify-1.5-py2.3.egg/collective/jsonify/export.py", line 266, in export_content
write(walk(self, skip_callback=skip_callback))
File "/home/software/python/2.3.5/lib/python2.3/site-packages/collective.jsonify-1.5-py2.3.egg/collective/jsonify/export.py", line 337, in write
for item in items:
File "/home/software/python/2.3.5/lib/python2.3/site-packages/collective.jsonify-1.5-py2.3.egg/collective/jsonify/export.py", line 299, in walk
item = folder.get(item_id)
AttributeError: get

[rpijlman]

Duplicate of #48

[ale-rt]

Sorry I missed you already opened an issue for this!