Jmeter - java.lang.NullPointerException when running a few users

Question

I've been working on jmeter stress tests, and found an issue that i'm not able to solve.

So if I run a testplan with an user all works peachy, I'm able to scale it until 25 simultaneous users.

As soon as I try to use 26 user using any ramp up I get the following error.

2014/01/06 11:17:19 ERROR - jmeter.threads.JMeterThread: Exception processing Assertion  java.lang.NullPointerException
    at org.apache.jmeter.assertions.ResponseAssertion.evaluateResponse(ResponseAssertion.java:329)
    at org.apache.jmeter.assertions.ResponseAssertion.getResult(ResponseAssertion.java:201)
    at org.apache.jmeter.threads.JMeterThread.processAssertion(JMeterThread.java:706)
    at org.apache.jmeter.threads.JMeterThread.checkAssertions(JMeterThread.java:677)
    at org.apache.jmeter.threads.JMeterThread.process_sampler(JMeterThread.java:439)
    at org.apache.jmeter.threads.JMeterThread.run(JMeterThread.java:256)
    at java.lang.Thread.run(Thread.java:722)

Thanks in advance

Answer 1

Line 329 in ResponseAssertion.java is following:

       if (toCheck.length() == 0) {

where toCheck can be response Data/URL/Code/Message/Headers/Ignore Status

I expect that you're trying to execute assertion against something which is null that's why it's failing.

The easiest way to debug it is View Results Tree Listener . If your test is too heavy and you cannot use it for some reasons you can try setting jmeter.save.saveservice.response_data.on_error=true property. This can be done in jmeter.properties file which lives under "/bin" folder of your JMeter installation. If you're running JMeter in non-GUI mode you can override this property via -J command line switch as follows:

jmeter -Jjmeter.save.saveservice.response_data.on_error=true -n -t "path_to_your_JTL_file" -l "path_to_your_JTL_file"

And inspect results JTL file for failure response details.

You can also try upgrading to JMeter 2.11 which has recently been announced and see if it resolves your issue.

But prior doing all above please double check that your application or web or database server or load balancer or whatever you use allows 25+ concurrent connections.

Answer 2

Upgrade to JMeter 2.11 this has been fixed:

• http://jmeter.apache.org/changes.html