3 files changed, 2 insertions, 5 deletions
diff --git a/src/org/traccar/Context.java b/src/org/traccar/Context.java
index 2afdde3b9..d607baf3e 100644
--- a/src/org/traccar/Context.java
+++ b/src/org/traccar/Context.java
@@ -87,9 +87,6 @@ import javax.ws.rs.client.ClientBuilder;
 
 public final class Context {
 
-    private static final String USER_AGENT =
-            "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:59.0) Gecko/20100101 Firefox/59.0";
-
     private Context() {
     }
 
diff --git a/src/org/traccar/protocol/RoboTrackFrameDecoder.java b/src/org/traccar/protocol/RoboTrackFrameDecoder.java
index aecbaaa3b..85ed6c76f 100644
--- a/src/org/traccar/protocol/RoboTrackFrameDecoder.java
+++ b/src/org/traccar/protocol/RoboTrackFrameDecoder.java
@@ -23,7 +23,7 @@ import org.traccar.BaseFrameDecoder;
 public class RoboTrackFrameDecoder extends BaseFrameDecoder {
 
     private int messageLength(ByteBuf buf) {
-        switch ((int) buf.getByte(buf.readerIndex())) {
+        switch (buf.getUnsignedByte(buf.readerIndex())) {
             case RoboTrackProtocolDecoder.MSG_ID:
                 return 69;
             case RoboTrackProtocolDecoder.MSG_ACK:
diff --git a/src/org/traccar/protocol/SabertekFrameDecoder.java b/src/org/traccar/protocol/SabertekFrameDecoder.java
index 771ef9cfb..ad5000bf8 100644
--- a/src/org/traccar/protocol/SabertekFrameDecoder.java
+++ b/src/org/traccar/protocol/SabertekFrameDecoder.java
@@ -29,7 +29,7 @@ public class SabertekFrameDecoder extends BaseFrameDecoder {
         int beginIndex = buf.indexOf(buf.readerIndex(), buf.writerIndex(), (byte) 0x02);
         if (beginIndex >= 0) {
             int endIndex = buf.indexOf(buf.readerIndex(), buf.writerIndex(), (byte) 0x03);
-            if (beginIndex >= 0) {
+            if (endIndex >= 0) {
                 buf.readerIndex(beginIndex + 1);
                 ByteBuf frame = buf.readRetainedSlice(endIndex - beginIndex - 1);
                 buf.readerIndex(endIndex + 1);