Exception occurs when exporting skeleton

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Open an armature-animated 3d model with blender. Such as 
http://www.blendswap.com/blends/view/72521
2. In object mode, shift-RMB select the mesh object and it's parent armature
3. File->Export->Ogre3D with option 'Only Deformable Bones' enabled.

What is the expected output? What do you see instead?
The exporter should export .mesh.xml and .skeleton.xml files correctly, but 
only mesh xml is produced. With the following error log:

Traceback (most recent call last):
  File "/home/levin/.config/blender/2.69/scripts/addons/io_export_ogreDotScene.py", line 3161, in execute
    self.ogre_export(self.filepath, context)
  File "/home/levin/.config/blender/2.69/scripts/addons/io_export_ogreDotScene.py", line 3599, in ogre_export
    xmlparent = doc._scene_nodes
  File "/home/levin/.config/blender/2.69/scripts/addons/io_export_ogreDotScene.py", line 3885, in _node_export
    xmlparent=o
  File "/home/levin/.config/blender/2.69/scripts/addons/io_export_ogreDotScene.py", line 3756, in _node_export
    self.dot_mesh( ob, os.path.split(url)[0] )
  File "/home/levin/.config/blender/2.69/scripts/addons/io_export_ogreDotScene.py", line 3392, in dot_mesh
    dot_mesh( ob, path, force_name, ignore_shape_animation=False )
  File "/home/levin/.config/blender/2.69/scripts/addons/io_export_ogreDotScene.py", line 5410, in dot_mesh
    skel = Skeleton( ob )
  File "/home/levin/.config/blender/2.69/scripts/addons/io_export_ogreDotScene.py", line 4477, in __init__
    for b in self.bones: b.rebuild_tree()
  File "/home/levin/.config/blender/2.69/scripts/addons/io_export_ogreDotScene.py", line 4415, in rebuild_tree
    self.parent.children.append( self )
AttributeError: 'NoneType' object has no attribute 'children'

location: <unknown location>:-1

What version of the product are you using? On what operating system?
Blender version: v2.69
blender2ogre version: blender2ogre-0.6.0
OS: Ubuntu 12.04.3 LTS

Please provide any additional information below.

Original issue reported on code.google.com by LevinJi...@gmail.com on 21 Apr 2014 at 1:35

[GoogleCodeExporter]

Uploaded the animated .blend file

Original comment by LevinJi...@gmail.com on 21 Apr 2014 at 1:42

Attachments:

• cartoonBoy_rigged_and_animated.blend

[GoogleCodeExporter]

Same error also reproducible in Blender v2.67

Original comment by LevinJi...@gmail.com on 21 Apr 2014 at 1:51