Unit's IComparable.CompareTo should throw ArgumentException when obj is not of type Unit

[vjacquet]

Hello,

As it is currently implemented, CompareTo always return 0, meaning equality, for objects of any type or even for null references. https://github.com/jbogard/MediatR/blob/a9e032dbf3d19aff0212fb12e4ba2c79450e61f4/src/MediatR.Contracts/Unit.cs#L47

This is inconsistent with Equals that correctly returns true only when the parameter is of the same type. https://github.com/jbogard/MediatR/blob/a9e032dbf3d19aff0212fb12e4ba2c79450e61f4/src/MediatR.Contracts/Unit.cs#L73

IComparable contract states that CompareTo throws ArgumentException when obj is not the same type as this instance.

A possible implementation could be

int IComparable.CompareTo(object? obj) => obj is Unit ? 0 : throw new ArgumentException();

[jbogard]

What issue is this causing for you?

[vjacquet]

None, but is it relevant? Well, I guess it is, because even though it is probably inconsequential, fixing it would be a breaking change.

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[github-actions[bot]]

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