How much null checking is enough?

Question

What are some guidelines for when it is not necessary to check for a null?

A lot of the inherited code I\'ve been working on as of late has null-checks

Answer 1

If you write the code and its contract, you are responsible for using it in terms of its contract and ensuring the contract is correct. If you say "returns a non-null" x, then the caller should not check for null. If a null pointer exception then occurs with that reference/pointer, it is your contract that is incorrect.

Null checking should only go to the extreme when using a library that is untrusted, or does not have a proper contract. If it is your development team's code, stress that the contracts must not be broken, and track down the person who uses the contract incorrectly when bugs occur.