Code Correctness: null Argument to equals()

Abstract
The expression obj.equals(null) should always be false.

Description
The program uses the equals method to compare an object with null. The contract of the equals method requires this comparison to always return false[1].

Reference
[1] Sun JavaDoc for Object. http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Object.html#equals(java.lang.Object)