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            Programs must not catch {{java.lang.NullPointerException}}. A {{NullPointerException}} exception thrown at runtime indicates the existence of an underlying {{null}} pointer dereference that must be fixed in the application code (see rule [EXP01-J. Never dereference null pointers] for more information). Handling the underlying null pointer dereference by catching the {{NullPointerException}} rather than fixing the underlying problem is inappropriate for several reasons. First, catching {{NullPointerException}} adds significantly more performance overhead than simply adding the necessary null checks \[[Bloch 2008|AA. Bibliography#BlochReferences#Bloch 08]\]. Second, when multiple expressions in a {{try}} block are capable of throwing a {{NullPointerException}}, it is difficult or impossible to determine which expression is responsible for the exception because the {{NullPointerException}} {{catch}} block handles any {{NullPointerException}} thrown from any location in the {{try}} block. Third, programs rarely remain in an expected and usable state after a {{NullPointerException}} has been thrown. Attempts to continue execution after first catching and logging (or worse, suppressing) the exception rarely succeed.

This noncompliant code example is derived from the logging service null object design pattern described by Henney \[[Henney 2003|AA. Bibliography#HenneyReferences#Henney 03]\]. The logging service is composed of two classes: one that prints the triggering activity's details to a disk file using the {{FileLog}} class and another that prints to the console using the {{ConsoleLog}} class. An interface, {{Log}}, defines a {{write()}} method that is implemented by the respective log classes. Method selection occurs polymorphically at runtime.  The logging infrastructure is subsequently used by a {{Service}} class.

Some system designs require returning a value from a method rather than implementing _do-nothing_ behavior. One acceptable approach is use of an exceptional value object that throws an exception before the method returns \[[Cunningham 1995|AA. Bibliography#CunninghamReferences#Cunningham 95]\]. This can be a useful alternative to returning {{null}}.

*ERR08-EX1:* Task processing threads such as worker threads in a thread pool or the Swing event dispatch thread are permitted to catch {{RuntimeException}} when they call untrusted code through an abstraction such as the {{Runnable}} interface \[[Goetz 2006|AA. Bibliography#GoetzReferences#Goetz 06], p. 161\].