[SEBA-946]

Fix Swagger documentation generation, update to Python 3

Change-Id: I0a55c4805a993dcac9f0721be87bbefbf8b9b348
diff --git a/lib/xos-genx/xosgenx/jinja2_extensions/base.py b/lib/xos-genx/xosgenx/jinja2_extensions/base.py
index 26564bb..5f24f40 100644
--- a/lib/xos-genx/xosgenx/jinja2_extensions/base.py
+++ b/lib/xos-genx/xosgenx/jinja2_extensions/base.py
@@ -482,7 +482,8 @@
         c_list = []
 
         for c in eval(xproto_unquote(f["options"]["choices"])):
-            c_list.append(c[0])
+            if c[0] is not None:
+                c_list.append(c[0])
 
         return sorted(c_list)
     else: