Incorrect description of `is var` behavior

[Zenexer]

https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/is#-var-pattern- states the following:

A pattern match with the var pattern always succeeds for non-null expressions; if expr is null, the is expression is false. The non-null value of expr is always assigned to a local variable the same type as the runtime time type of expr. Its syntax is:

expr is var varname

The following example uses the var pattern to assign an expression to a variable named obj. It then displays the value and the type of obj.

It then provides an example, of which the key component is the following:

object[] items = { new Book("The Tempest"), new Person("John") };
foreach (var item in items) {
if (item is var obj)
  Console.WriteLine($"Type: {obj.GetType().Name}, Value: {obj}"); 
}

This very clearly and unambiguously indicates that item is var obj will return false if item is null. This assertion is incorrect, and there are multiple references, including on https://github.com/dotnet/csharplang, stating that is var will always return true, regardless of nullability.

This error seems to be the cause of some confusion:

• https://stackoverflow.com/questions/45844586/usage-of-var-pattern-in-c-sharp-7/55646164
• Is-expressions w/ patterns: Why is var allows nulls through? csharplang#981

There was a proposal to add this behavior, but it was declined: dotnet/csharplang#792

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Document Details

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• ID: 3126aaa9-8f5f-04f3-2d75-96477b6273cd
• Version Independent ID: 3f4b3eac-11eb-2dd6-4f27-b24537367288
• Content: is - C# Reference
• Content Source: docs/csharp/language-reference/keywords/is.md
• Product: dotnet-csharp
• GitHub Login: @BillWagner
• Microsoft Alias: wiwagn

[Thraka]

@BillWagner I just verified that is var does indeed always return true. I tested both c# 7.3 and 8.0.