how to read Rawrequest using Script Assertion while using URI formats in the request ..

My request is in URI format and not Xml. Now i need to read the rawrequest using Script Assertion. I tried this below piece of code. It is working at the Groovy level. But when i used this in Script Assertion (at the teststep level) it is failing.. i'm not getting the result

def request = testRunner.testCase.getTestStepByName("Request").getHttpRequest().getRequestContent()