2 files changed, 9 insertions, 2 deletions
diff --git a/src/main/java/org/traccar/protocol/MictrackProtocolDecoder.java b/src/main/java/org/traccar/protocol/MictrackProtocolDecoder.java
index 0f815ca7b..ec4f97919 100644
--- a/src/main/java/org/traccar/protocol/MictrackProtocolDecoder.java
+++ b/src/main/java/org/traccar/protocol/MictrackProtocolDecoder.java
@@ -209,8 +209,12 @@ public class MictrackProtocolDecoder extends BaseProtocolDecoder {
     }
 
     private Object decodeLowAltitude(
-            Channel channel, SocketAddress remoteAddress, String sentence) throws Exception {
-        String deviceId = sentence.substring(0, sentence.indexOf("$"));
+            Channel channel, SocketAddress remoteAddress, String sentence) {
+        int separator = sentence.indexOf("$");
+        if (separator < 0) {
+            return null;
+        }
+        String deviceId = sentence.substring(0, separator);
 
         DeviceSession deviceSession = getDeviceSession(channel, remoteAddress, deviceId);
         if (deviceSession == null) {
diff --git a/src/test/java/org/traccar/protocol/MictrackProtocolDecoderTest.java b/src/test/java/org/traccar/protocol/MictrackProtocolDecoderTest.java
index 605a02b92..22f0974ec 100644
--- a/src/test/java/org/traccar/protocol/MictrackProtocolDecoderTest.java
+++ b/src/test/java/org/traccar/protocol/MictrackProtocolDecoderTest.java
@@ -10,6 +10,9 @@ public class MictrackProtocolDecoderTest extends ProtocolTest {
 
         MictrackProtocolDecoder decoder = new MictrackProtocolDecoder(null);
 
+        verifyNull(decoder, text(
+                "mode=Success!"));
+
         verifyPosition(decoder, text(
                 "MT;6;866425031361423;R0;10+190109091803+22.63827+114.02922+2.14+69+2+3744+113"),
                 position("2019-01-09 09:18:03.000", true, 22.63827, 114.02922));