how to collect assertion message from Assertion Teststep

With help from Smartbear support I found the solution. For assertion test step the code to collect assertion messages is slightly different: see below...

public static String getTestCaseRunAssertionMessages( def testRunner, def context, def log ) {
	log.debug "*** Method getTestCaseRunAssertionMessages ***"
	def testStepList = testRunner.getTestCase().getTestStepList()
	String assertErrors = ""
	if (context.requestAttempt >= 3 ) {
		assertErrors = "Stop processing after " + context.requestAttempt + " request attempts";
	}
	testStepList.each {
		if ( it.isDisabled() == false ) {
			log.debug it.getClass()
			// Collecting assertion messages differs from AssertionTestStep and wsdl/rest steps
			if ( it.getClass().toString().contains( "AssertionTestStep") ) {
				log.debug "*** AssertionTestStep ***"
				def list = it.getAssertionEntryList()
				for( assertion in list) {
					for (err in assertion.getAssertion().getErrors()) {
						log.debug "Failed assertions found in: " + it.getName();
						if ( assertErrors.equals("") ) {
							assertErrors = it.name + ": " + err.getMessage();
						} else {
							assertErrors = assertErrors + "\n" + it.name + ": " + err.getMessage();
						}
					}
				}
			} else if ( it.metaClass.hasProperty( it, 'assertionStatus' ) ) {
				log.debug "Collecting assertion messages in: " + it.getName();
				for( assertion in it.assertionList ) {
					for( e in assertion.errors ) {
						log.debug "Failed assertions found in: " + it.getName();
						if ( assertErrors.equals("") ) {
							assertErrors = it.name + ": " + e.message;
						} else {
							assertErrors = assertErrors + "\n" + it.name + ": " + e.message;
						}
					}
				}
			}
		}
	}
	return assertErrors