Here you can find the source of assertNotNull(Object expression)
private static void assertNotNull(Object expression)
//package com.java2s; //License from project: Apache License public class Main { public static final String TRANSFORM_WITHOUT_CHECK = "Expression must be checked before applying transformation"; private static void assertNotNull(Object expression) { assert expression != null : TRANSFORM_WITHOUT_CHECK; }/*from ww w.j a v a 2 s . c o m*/ }