Fixed error: metadata cant be NoneType

src/metadata.py

@@ -84,6 +84,8 @@ def get_metadata_keys(obj):
 
 def set_metadata(obj, key, value):
     # TODO: Fix this with upgrade to py3
+    if value is None:
+        return
     try:
         obj.setMetaData(key, value)
     except UnicodeEncodeError: