diff --git a/lib/oto/commands/util/slack.dart b/lib/oto/commands/util/slack.dart
index 1d875d9..350679d 100644
--- a/lib/oto/commands/util/slack.dart
+++ b/lib/oto/commands/util/slack.dart
@@ -16,7 +16,11 @@ class Slack extends Command {
     var sender = SlackSender(data.token);
     DataSlack? message = null;
     if(data.property != null) {
-      message = replaceSingleTag(data.property!) as DataSlack;
+      var value = replaceSingleTag(data.property!);
+      if(value != null)
+      {
+        message = value as DataSlack;
+      }
     } else if(data.message != null) {
       message = data.message;
     }