Update RELEASE_NOTES.md for 1.0.4 release · akkadotnet/reactive-streams-dotnet@7f2e1a7

Non-nullable field '_subscription' must contain a non-null value when exiting constructor. Consider declaring the field as nullable.

Non-nullable field '_enumerator' must contain a non-null value when exiting constructor. Consider declaring the field as nullable.

Non-nullable field '_subscription' must contain a non-null value when exiting constructor. Consider declaring the field as nullable.

Possible null reference return.

XML comment has cref attribute 'AtomicReference{T}' that could not be resolved

Non-nullable field '_enumerator' must contain a non-null value when exiting constructor. Consider declaring the field as nullable.

Possible null reference return.

Cannot convert null literal to non-nullable reference type.

Possible null reference argument for parameter 'element' in 'void ISubscriber<T>.OnNext(T element)'.

Cannot convert null literal to non-nullable reference type.

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