Add docstrings to globalmessages data interface

endpoints/api/globalmessages_models_pre_oci.py

@@ -8,13 +8,21 @@ class GlobalMessagePreOCI(GlobalMessageDataInterface):
     messages = model.message.get_messages()
     return [self._message(m) for m in messages]
   
-  def create_message(self, content):
-    model.message.create([content])
+  def create_message(self, severity, media_type_name, content):
+    message = {
+      'severity': severity,
+      'media_type': media_type_name,
+      'content': content
+    }
+    messages = model.message.create([message])
+    return self._message(messages[0])
   
   def delete_message(self, uuid):
     model.message.delete_message([uuid])
   
   def _message(self, message_obj):
+    if message_obj is None:
+      return None
     return GlobalMessage(
       uuid=message_obj.uuid,
       content=message_obj.content,