Can't able to Read Data from method readDLMSPacket(byte[] data, GXReplyData reply)

first time i can able to read data second time if i want to read data i am facing issue

Some times i am getting data.length 0 , and some time if data length grater then 0 also i am not getting data Exception as

java.lang.RuntimeException: java.lang.IllegalArgumentException: Data send failed.

java.lang.NullPointerException: Attempt to get length of null array

public void readDLMSPacket(byte[] data, GXReplyData reply) throws Exception {

System.out.println("==data"+data.length);
if (data == null || data.length == 0) {
return;
}

IGXMedia media = mDevice.getMedia();
reply.setError((short) 0);
Object eop = (byte) 0x7E;
Integer pos = 0;
boolean succeeded = false;
ReceiveParameters<byte[]> p =
new ReceiveParameters<byte[]>(byte[].class);
p.setEop(eop);
p.setCount(5);
p.setWaitTime(mDevice.getWaitTime() * 1000);
synchronized (media.getSynchronous()) {
while (!succeeded) {
writeTrace("<- " + now() + "\t" + GXCommon.bytesToHex(data));
System.out.print(now() + "Tx:" + "\t" + GXCommon.bytesToHex(data));
System.out.println();
media.send(data, null);
if (p.getEop() == null) {
p.setCount(1);
}
succeeded = media.receive(p);

if (!succeeded) {
// Try to read again...
if (pos++ == 3) {
throw new RuntimeException("Failed to receive reply from the device in given time.");
}
AlertClass.alert_("Data send failed. Try to resend " + pos.toString() + "/3",getApplicationContext());
System.out.println("Data send failed. Try to resend " + pos.toString() + "/3");
}
}
// Loop until whole DLMS packet is received.
try {
while (!mClient.getData(p.getReply(), reply)) {
if (p.getEop() == null) {
p.setCount(1);
}
if (!media.receive(p)) {
// If echo.
if (reply.isEcho()) {
media.send(data, null);
}
// Try to read again...
if (++pos == 3) {
throw new Exception(
"Failed to receive reply from the device in given time.");
}
AlertClass.alert_("Data send failed3. Try to resend" + pos.toString() + "/3",getApplicationContext());

System.out.println("Data send failed. Try to resend " + pos.toString() + "/3");
}
}
} catch (Exception e) {
System.out.println("readDLMSPacket_exeption");
Log.d("==data", String.valueOf( now() + "\t" + GXCommon.bytesToHex(p.getReply())));
writeTrace("-> " + now() + "\t" + GXCommon.bytesToHex(p.getReply()));
System.out.print(now()+"RxE:" + "\t" + GXCommon.bytesToHex(p.getReply()));
System.out.println();
throw e;
}

}
writeTrace("-> " + now() + "\t" + GXCommon.bytesToHex(p.getReply()));
System.out.print(now()+"Rx:" + "\t" + GXCommon.bytesToHex(p.getReply()));
System.out.println();

if (reply.getError() != 0) {
if (reply.getError() == ErrorCode.REJECTED.getValue()) {
Thread.sleep(1000);
readDLMSPacket(data, reply);
} else {
System.out.println("Data send failed. Try to resend once ");
// throw new GXDLMSException(reply.getError());
}
}
// readDLMSPacket(mClient.keepAlive(), reply);
}