Generated extension methods do not correctly handle optional array parameters

[BasTossings]

Actual behavior

For example, the generated extension for ID2D1Factory.CreateStrokeStyle is as follows:

internal static unsafe void CreateStrokeStyle(this winmdroot.Graphics.Direct2D.ID2D1Factory @this, in winmdroot.Graphics.Direct2D.D2D1_STROKE_STYLE_PROPERTIES strokeStyleProperties, float[] dashes, out winmdroot.Graphics.Direct2D.ID2D1StrokeStyle strokeStyle)
	{
	fixed (winmdroot.Graphics.Direct2D.D2D1_STROKE_STYLE_PROPERTIES* strokeStylePropertiesLocal = &strokeStyleProperties)
		{
		@this.CreateStrokeStyle(strokeStylePropertiesLocal, dashes, (uint )dashes.Length, out strokeStyle);
		}
	}

The official API documentation states dashes is [in, optional].

when you call CreateStrokeStyle with dashes set to null, you get a NullReferenceException on (uint )dashes.Length.

Expected behavior

The generated extension methods should test for null on optional array parameters.

Repro steps

1. NativeMethods.txt content:

ID2D1Factory

2. NativeMethods.json content (if present):

{
  "$schema": "https://aka.ms/CsWin32.schema.json",
  "public": false,
  "allowMarshaling": true
}

3. Any of your own code that should be shared?

Context

• CsWin32 version: 0.3.18-beta
• Win32Metadata version (if explicitly set by project): n/a
• Target Framework: net7.0
• LangVersion (if explicitly set by project): n/a

[AArnott]

Thanks for the excellent report.