> In a Java program, a variable of type String may hold either a reference to a String object or the special value null. In some cases, the author intends that

> In a Java program, a variable of type String may hold either a reference to a String object or the special value null. In some cases, the author intends that the variable will always hold a reference to a String object; in other cases, the author expects null as a meaningful value. Unfortunately, there is no way to formally express in the language which of these alternatives is intended, leading to confusion and bugs. Casually just describes one of the largest sources of bugs in the history of programming.