foo.diff

diff --git a/debezium-core/src/main/java/io/debezium/relational/topic/TopicMappers.java b/debezium-core/src/main/java/io/debezium/relational/topic/TopicMappers.java
index 5cdfcab..eb05251 100644
--- a/debezium-core/src/main/java/io/debezium/relational/topic/TopicMappers.java
+++ b/debezium-core/src/main/java/io/debezium/relational/topic/TopicMappers.java
@@ -28,10 +28,11 @@ public TopicMappers(Configuration config, String[] topicMapperAliases) {
         if (topicMapperAliases != null) {
             for (String alias : topicMapperAliases) {
                 TopicMapper topicMapper = config.getInstance("topic.mappers." + alias + ".type", TopicMapper.class);
-                if (topicMapper != null) {
-                    topicMappers.add(topicMapper);
-                    validateTopicMapperConfig(topicMapper, alias, config);
+                if (topicMapper == null) {
+                    throw new ConnectException("Unable to instantiate topic mapper class for alias: " + alias);
                 }
+                topicMappers.add(topicMapper);
+                validateTopicMapperConfig(topicMapper, alias, config);
             }
         }
         TopicMapper defaultTopicMapper = new ByTableTopicMapper();