# HG changeset patch
# User drewp@bigasterisk.com
# Date 1631901793 25200
# Node ID c04b5303eb081ae12a4693fa03eb6101d616fe75
# Parent  78024b27f9ec030e5513dc02a4f3a78960122fb2
try not to make empty topic subscriptions

diff -r 78024b27f9ec -r c04b5303eb08 service/mqtt_to_rdf/mqtt_to_rdf.py
--- a/service/mqtt_to_rdf/mqtt_to_rdf.py	Fri Sep 17 11:01:06 2021 -0700
+++ b/service/mqtt_to_rdf/mqtt_to_rdf.py	Fri Sep 17 11:03:13 2021 -0700
@@ -224,6 +224,10 @@
     return n3
 
 
+class EmptyTopicError(ValueError):
+    pass
+
+
 class MqttStatementSource:
 
     def __init__(self, uri: URIRef, config: Graph, masterGraph: PatchableGraph, mqtt, internalMqtt, debugPageData,
@@ -238,6 +242,8 @@
         self.inference = inference
 
         self.mqttTopic = self.topicFromConfig(self.config)
+        if self.mqttTopic == b'':
+            raise EmptyTopicError(f"empty topic for {uri=}")
         log.debug(f'new mqttTopic {self.mqttTopic}')
 
         self.debugSub = {