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Home/ Questions/Q 6551435
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Editorial Team
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Editorial Team
Asked: May 25, 20262026-05-25T12:20:17+00:00 2026-05-25T12:20:17+00:00

IDictionary<TKey, TValue> ArgumentNullException – key is null. Then, in the remarks… Implementations can vary

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IDictionary<TKey, TValue>

ArgumentNullException – key is null.

Then, in the remarks…

Implementations can vary in whether they allow key to be null.

So, I have to wonder… is this an error or something I’m just missing here? The MSDN help file seems a bit contradictory.

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  1. Editorial Team
    Editorial Team
    2026-05-25T12:20:18+00:00Added an answer on May 25, 2026 at 12:20 pm

    What the documentation says is “If you get ArgumentNullException, then key was null”.

    It does not say “If key is null, you get an ArgumentNullException.” That would be an converse logic fallacy.

    The complete condition would be:

    “If and only if both key is null and the container does not support null keys, you get an ArgumentNullException.”

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