While using ReadSerialTest inside the package com.serotonin.modbus4j.test, I am getting the error mentioned below for Modbus RTU over RS232.
at com.serotonin.modbus4j.sero.messaging.InputStreamListener.run

Actually the software doesn't transmit any data over RS232. Hence its receiving a null pointer exception on the receive side.
Output stream this.out is null, not assigned.
public StreamTransport(InputStream in, OutputStream out) {
this.out = out;
this.in = in;
}

What could be the reason. Please help me to resolve the problem.

Thank you so much it works.

    BatchRead<Integer> batch = new BatchRead<Integer>();
    int add;
    int reg;
    int typ;
    add = FEOHdb.intDB[1][3];
   for (int m = 1 ; m < FEOHdb.tDev; m++){
	   add = FEOHdb.intDB[m][3];
   
    for (int n = 1; n < FEOHdb.mapQty; n++ ){
    reg =FEOHdb.mapInt[n][1];
    typ =FEOHdb.mapInt[n][2];
   	batch.addLocator(n-1, BaseLocator.holdingRegister(add, reg, typ));
    }
}
    

    try {
        master.init();

        while (pool) {
            batch.setContiguousRequests(false);
            BatchResults<Integer> results = master.send(batch);
                        
            for (int n = 0; n < FEOHdb.mapQty; n++){ 
            	System.out.println("Value =  " + (int) results.getValue(n));
            }
            Thread.sleep(500);
       
        }