混淆报错，请问我该怎么处理

[aa563011992]

W/IModbusWorker: ModbusMaster init failed com.serotonin.modbus4j.exception.ModbusInitException: java.lang.NullPointerException at com.serotonin.modbus4j.serial.SerialMaster.init(SourceFile:84) at com.serotonin.modbus4j.serial.rtu.RtuMaster.init(SourceFile:71) at com.licheedev.modbus4android.ModbusWorker$5.call(SourceFile:299) at com.licheedev.modbus4android.ModbusWorker$5.call(SourceFile:281) at java.util.concurrent.FutureTask.run(FutureTask.java:237) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) at java.lang.Thread.run(Thread.java:841) Caused by: java.lang.NullPointerException at java.io.File.fixSlashes(File.java:185) at java.io.File.(File.java:134) at android.serialport.SerialPort$Builder.(SourceFile:147) at android.serialport.SerialPort$Builder.(SourceFile:132) at android.serialport.SerialPort.newBuilder(SourceFile:129) at com.licheedev.modbus4android.AndroidSerialPortWrapper.open(SourceFile:72) at com.serotonin.modbus4j.serial.SerialMaster.init(SourceFile:75) at com.serotonin.modbus4j.serial.rtu.RtuMaster.init(SourceFile:71)  at com.licheedev.modbus4android.ModbusWorker$5.call(SourceFile:299)  at com.licheedev.modbus4android.ModbusWorker$5.call(SourceFile:281)  at java.util.concurrent.FutureTask.run(FutureTask.java:237)  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)  at java.lang.Thread.run(Thread.java:841) 

modbus

-keep class com.licheedev. { *; } -keep class com.serotonin.* { ; } -keep class android.serialport. { *; }