Issues running in python script

[Sheena Kiran]

I have 2 IoT nodes, IOT1 and IOT2. IOT1 send messages to IOT2.

Python scipt of IOT1 is 

import time

while node.loop():
        node.send(x)
        x = x+5

Python script of IOT2

import time
while node.loop():
        n = node.bufferSize()
        if n>0:
                x = node.read()
                node.print(x)
        time.sleep(0.01)

But while running the simulation it shows an error. Java.lang.nullpointerexception

How can I resolve it.. Pls help me