[Ready API 1.2] NullPointerException when exporting failed test result

I get the following exception in a lot of my tests, when running them in headless mode with Ready API 1.2.

Any idea what the problem is? Could there be a problem in my test cases or configuration?

14:39:16,478 ERROR [SoapUIProTestCaseRunner] ASSERTION FAILED -> Assertion failed for path [$.GROUP[0].CMD] : PathNotFoundException:Array index [Ljava.lang.String;@2ac1e10f not found in path
14:39:16,478 ERROR [SoapUIProTestCaseRunner] Check something failed, exporting to [C:\myworkspace\Report\TS-TC-Check_something-0-FAILED.txt]
14:39:16,481 ERROR [SoapUIProTestCaseRunner] Error saving failed result: java.lang.NullPointerException
java.lang.NullPointerException
    at com.eviware.soapui.impl.wsdl.teststeps.RestRequestStepResult.writeTo(RestRequestStepResult.java:212)
    at com.smartbear.ready.cmd.runner.SoapUITestCaseRunner.afterStep(SoapUITestCaseRunner.java:666)
    at com.eviware.soapui.impl.wsdl.support.AbstractTestCaseRunner.notifyListenersAfterStep(AbstractTestCaseRunner.java:254)
    at com.eviware.soapui.impl.wsdl.support.AbstractTestCaseRunner.runTestStep(AbstractTestCaseRunner.java:231)
    at com.eviware.soapui.impl.wsdl.testcase.WsdlTestCaseRunner.runCurrentTestStep(WsdlTestCaseRunner.java:47)
    at com.eviware.soapui.impl.wsdl.support.AbstractTestCaseRunner.internalRun(AbstractTestCaseRunner.java:145)
    at com.eviware.soapui.impl.wsdl.support.AbstractTestCaseRunner.internalRun(AbstractTestCaseRunner.java:1)
    at com.eviware.soapui.impl.wsdl.support.AbstractTestRunner.run(AbstractTestRunner.java:130)
    at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
    at java.util.concurrent.FutureTask.run(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
14:39:16,489 ERROR [AbstractTestCaseRunner] Error notifying listener

Nb: I had to manually modify the name of the test suites / cases / steps in the log before pasting them here - I assume they are not related to the cause of the error anyway.