NullReferenceException in ImmutableArray.ToBuilder

[lindexi]

Description

The ImmutableArray.ToBuilder will throw System.NullReferenceException:“Object reference not set to an instance of an object.” with the stacktrace as

 	System.Collections.Immutable.dll!System.Collections.Immutable.ImmutableArray<int>.Length.get()
 	System.Collections.Immutable.dll!System.Collections.Immutable.ImmutableArray<int>.ToBuilder()
>	GijachekecuYichearcalallnair.dll!Program.<Main>$(string[] args = {string[0]}) 

Reproduction Steps

Mini repro code:

using System.Collections.Immutable;
var immutableArray = new ImmutableArray<int>();
var builder = immutableArray.ToBuilder();

You can find all my code in https://github.com/lindexi/lindexi_gd/tree/61fa97cc6b5ea61c280364848829beef9f768bdf/Workbench/GijachekecuYichearcalallnair

Expected behavior

It can return the ImmutableArray<T>.Builder object.

Actual behavior

Throw the NullReferenceException.

Regression?

No response

Known Workarounds

No response

Configuration

dotnet --info

.NET SDK:
Version: 9.0.203
Commit: dc7acfa194
Workload version: 9.0.200-manifests.47fce8c7
MSBuild version: 17.13.20+a4ef1e90f

Other information

Reference:

• ImmutableArray list initialiser throws NullReferenceException #26880
• Getting rid of ImmutableArray<T>.IsDefault ? #26829

The correct way of using it should be:

var builder = ImmutableArray.CreateBuilder<int>();

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[huoyaoyuan]

This is expected. Uninitialized ImmutableArray is the same as uninitialized reference type. See #98300.

[lindexi]

Thank you @huoyaoyuan . How about add the Parameterless constructor to ImmutableArray<T>?

runtime/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableArray_1.Minimal.cs

Lines 61 to 64 in 0d20f9a

	internal ImmutableArray(T[]? items)
	{
	this.array = items;
	}

And I find the design as #98300 says in comment:

runtime/src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableArray_1.Minimal.cs

Lines 142 to 144 in 0d20f9a

	// We intentionally do not check this.array != null, and throw NullReferenceException
	// if this is called while uninitialized.
	// The reason for this is perf.

[huoyaoyuan]

How about add the Parameterless constructor to ImmutableArray<T>?

I think it's not an allowed source-breaking change. It's also less valuable now since you can acquire the empty instance with [].

[lindexi]

Yes, you are right. Using [] can make the short code and more beneficial.

[eiriktsarpalis]

Duplicate of #98300