More general solution to word cloud export problems.

common/lib/xmodule/xmodule/raw_module.py

@@ -20,6 +20,8 @@ class RawDescriptor(XmlDescriptor, XMLEditingDescriptor):
         return {'data': etree.tostring(xml_object, pretty_print=True, encoding='unicode')}, []
 
     def definition_to_xml(self, resource_fs):
+        if not self.data:
+            return etree.fromstring('<{0} />'.format(self.category))
         try:
             return etree.fromstring(self.data)
         except etree.XMLSyntaxError as err:

common/lib/xmodule/xmodule/video_module.py

@@ -130,13 +130,6 @@ class VideoDescriptor(VideoFields,
         _parse_video_xml(video, video.data)
         return video
 
-    def definition_to_xml(self, resource_fs):
-        """
-        Override the base implementation. We don't actually have anything in the 'data' field
-        (it's an empty string), so we just return a simple XML element
-        """
-        return etree.Element('video')
-
 
 def _parse_video_xml(video, xml_data):
     """

common/lib/xmodule/xmodule/word_cloud_module.py

@@ -9,8 +9,6 @@ If student have answered - words he entered and cloud.
 import json
 import logging
 
-from lxml import etree
-
 from pkg_resources import resource_string
 from xmodule.raw_module import RawDescriptor
 from xmodule.editing_module import MetadataOnlyEditingDescriptor
@@ -246,9 +244,3 @@ class WordCloudDescriptor(WordCloudFields, MetadataOnlyEditingDescriptor, RawDes
     """Descriptor for WordCloud Xmodule."""
     module_class = WordCloudModule
     template_dir_name = 'word_cloud'
-
-    def definition_to_xml(self, resource_fs):
-        """
-        Since there's no real data, just return an empty XML tag.
-        """
-        return etree.fromstring('<word_cloud />')