Merge pull request #7561 from edx/mobile/PLAT-520

PLAT-520 Fix Asset store import of null values.

common/lib/xmodule/xmodule/assetstore/__init__.py

@@ -195,6 +195,9 @@ class AssetMetadata(object):
                 elif tag == 'locked':
                     # Boolean.
                     value = True if value == "true" else False
+                elif value == 'None':
+                    # None.
+                    value = None
                 elif tag in ('created_on', 'edited_on'):
                     # ISO datetime.
                     value = dateutil.parser.parse(value)
@@ -204,9 +207,6 @@ class AssetMetadata(object):
                 elif tag == 'fields':
                     # Dictionary.
                     value = json.loads(value)
-                elif value == 'None':
-                    # None.
-                    value = None
                 setattr(self, tag, value)
 
     @contract(node='AssetElement')

common/lib/xmodule/xmodule/assetstore/tests/test_asset_xml.py

@@ -57,6 +57,18 @@ class TestAssetXml(unittest.TestCase):
             new_value = getattr(new_asset_md, attr)
             self.assertEqual(orig_value, new_value)
 
+    def test_export_with_None_value(self):
+        """
+        Export and import a single AssetMetadata to XML with a None created_by field, without causing an exception.
+        """
+        asset_md = AssetMetadata(
+            self.course_id.make_asset_key('asset', 'none_value'),
+            created_by=None,
+        )
+        asset = etree.Element("asset")
+        asset_md.to_xml(asset)
+        asset_md.from_xml(asset)
+
     def test_export_all_assets_to_xml(self):
         """
         Export all AssetMetadatas to XML and verify the structure and fields.