How to get the assertion data in SoapUI using Groovy script?

Question

enter image description here

I have a SOAP request. Some times it gives a null/empty response. I have added assertion for the request and I am getting the assertion status and description. But how can I get the message "null/empty response"(screen shot of the message is attached) using the Groovy script.

def assertionsList = testRunner.getTestCase().getTestStepByName(""+testStep[i]+"").getAssertionList()

assertioncounter = assertionsList.size()

for( e in assertionsList){                                        
     log.info e.status
     log.info e.DESCRIPTION
    }