java.lang.NullPointerException: Cannot get property: value on null object

Hi,
      I am running my very first groovy script inside SoapUI. I get the error mentioned in the subject of this message. Here is the code I used ( which I copied from the SoapUI User guide ):
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def request = testRunner.testCase.getTestStepByName( "Groovy Script" );
def property = request.getProperty( "request" );

// parse out textnodes to modify
def node = new groovy.util.XmlParser(false,false).parseText(property.value);
def textNodes = node["soapenv:Body"]["sam:getContactInfo"]["String_1"][0].children()

// modify
textNodes.clear();
textNodes.add( "test" + System.currentTimeMillis() );

// write back to string
def writer = new java.io.StringWriter();
def printer = new groovy.util.XmlNodePrinter( new PrintWriter( writer ));
printer.print( node );

// set property
property.setValue( writer.toString() )
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What am I doing wrong? Should I have to set something before I run my script? I get this error even if I run the load test from the command line.

Also, is there a place I can go to for seeing working examples of groovy scripts inside SoapUI. I want to call different methods inside a Webservice and the inputs to successive webservice calls will be based on the responses to previous webservice calls.

Any help you can provide will be greatly appreciated.

Thanks,

Venkat