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Where null gets in

Code that passes every test and throws in production. Make the compiler find it.

Beginner18 min on the clock5 graded checks · 100 pointsC# Foundations

Graded by reading your code against the checklist below.

What you build

Say in the signature which things are allowed to be null
Reach through a possibly-missing value safely
Supply a fallback rather than returning null
Reject a null argument at the door, with a message
Do not silence the compiler with the null-forgiving !

Done means

No path through this method can dereference null.

How it is graded

Published in full, before you start — every point is one of these and there is nothing else.

Annotate what is allowed to be null+25Null, and where it gets in
Reach through it safely+20Null, and where it gets in
Supply a fallback instead of returning null+20Null, and where it gets in
No null-forgiving operator+20Null, and where it gets in
Reject a null argument at the door+15Null, and where it gets in

What it teaches

Null, and where it gets inbeginner

NullReferenceException is the most common crash in .NET; nullable annotations move the argument about what can be null from runtime to the compiler, before a user ever sees it.

The rest of C# Foundations

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