setting content-type header for mockservice

Hi,
Iam a newbie to soapui.Iam trying to have a mockserver running as part of my soapui tests.This mockserver doesnt have any operations and so iam writing some groovy code inside onRequestScript

def queryString = mockRequest.getHttpRequest().getQueryString()
def httpResponse = mockRequest.httpResponse
httpResponse.addHeader("Content-Type","application/json")

mockRunner.returnFile(httpResponse,new File('response.json'))
return new com.eviware.soapui.impl.wsdl.mock.WsdlMockResult(mockRequest)

So i have a question
For some reasons,content-type is being set as text/javascript(I cant seem to override it using groovy code)?

I followed following article
http://www.soapui.org/Service-Mocking/m ... vices.html


Thanks