Question

For a constructor with a single parameter, is it OK to throw an ArgumentNullException inside the constructor if the parameter is null/empty? OR, should it be thrown in the method that actually uses the argument? Thanks.

Answer 1

Yes, if it is completely essential then throw the exception. You should not* throw the exception later.

Always remember the “Fail Early Principle”. Concept being fail now, so you don’t waste time debugging or experience unexpected system functionality.

Alternatively you could also throw a ArgumentException for “” and ArgumentNullException for null. In either case make sure you throw a valid Exception message.

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Always a good reference article for managing exceptions: Good Exception Management Rules of Thumb

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Side note on what @Steve Michelotti said (because i am a huge fan of CodeContracts)

Contract.Requires<ArgumentNullException>(inputParemeter!= null, "inputparameter cannot be null");
Contract.Requires<ArgumentException>(inputParemeter!= "", "inputparameter cannot be empty string");

alternatively

Contract.Requires<ArgumentNullException>(!string.IsNullOrEmpty(inputParemeter), "inputparameter cannot be null or empty string");