Create a default placeholder if not existing.

bt5/erp5_opcua/SkinTemplateItem/portal_skins/erp5_opcua/ERP5Site_handleOPCUARequest.py

 """
 OPCUA to ERP5 OPCUA Document setter / getter glue script.
 """
+
 import json
 from erp5.component.module.Log import log
 
@@ -19,7 +20,11 @@ def convertNodeValue(node_id, node_value):
   return node_value
 
 # XXX: what should be the OPCUA container?
-default_opcua_document = context.opcua_document_module["1"]
+default_id = "1"
+default_opcua_document = context.opcua_document_module.get(default_id, None)
+if default_opcua_document is None:
+  context.opcua_document_module.newContent(portal_type = "OPCUA Document",
+                                           id = default_id)
 
 # do selection of oepration in a REST fashion based in HTTP method
 http_method = context.REQUEST.method