Need to delete datasource properties via groovy

but im receiving a class cast exception

List<com.eviware.soapui.model.testsuite.TestProperty> previousProperties = (ArrayList<com.eviware.soapui.model.testsuite.TestProperty>)testRunner.testCase.testSteps['Spreadsheet'].getPropertyList();
for(int j=0; j<previousProperties.size(); j++)
{
String propertyName = previousProperties.get(j).getName();
testRunner.testCase.testSteps['Spreadsheet'].removeProperty(propertyName);
}


can you help us guys?