MTOUCH : error MT2101: Can't resolve the reference 'System.Void System.Diagnostics.CodeAnalysis.NotNullAttribute::.ctor()', referenced from the method 'System.Void TestLib.Check::NotNull(System.Object)' in 'netstandard, Version=2.1.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.
Done building target "_CompileToNative" in project "TestApp.csproj" -- FAILED.

=== Visual Studio Community 2019 for Mac ===

Version 8.3 (build 1805)
Installation UUID: 810f3bf8-337b-43c5-bf8f-395e1eb8f7d6
	GTK+ 2.24.23 (Raleigh theme)
	Xamarin.Mac 5.16.1.24 (d16-3 / 08809f5b)

	Package version: 604000198

=== Mono Framework MDK ===

Runtime:
	Mono 6.4.0.198 (2019-06/fe64a4765e6) (64-bit)
	Package version: 604000198

=== NuGet ===

Version: 5.3.0.6192

=== .NET Core SDK ===

SDK: /usr/local/share/dotnet/sdk/3.0.100/Sdks
SDK Versions:
	3.0.100
	3.0.100-rc1-014190
	2.2.301
	2.2.300
	2.1.700
MSBuild SDKs: /Library/Frameworks/Mono.framework/Versions/6.4.0/lib/mono/msbuild/Current/bin/Sdks

=== .NET Core Runtime ===

Runtime: /usr/local/share/dotnet/dotnet
Runtime Versions:
	3.0.0
	3.0.0-rc1-19456-20
	2.2.6
	2.2.5
	2.1.13
	2.1.11

=== Xamarin.Profiler ===

Version: 1.6.12.26
Location: /Applications/Xamarin Profiler.app/Contents/MacOS/Xamarin Profiler

=== Updater ===

Version: 11

=== Apple Developer Tools ===

Xcode 11.0 (14936)
Build 11A420a

=== Xamarin.Mac ===

Version: 6.2.0.42 (Visual Studio Community)
Hash: 5e8a208b
Branch: d16-3
Build date: 2019-09-17 14:19:30-0400

=== Xamarin.iOS ===

Version: 13.2.0.42 (Visual Studio Community)
Hash: 5e8a208b
Branch: d16-3
Build date: 2019-09-17 14:19:30-0400

=== Xamarin Designer ===

Version: 16.3.0.230
Hash: bbe518670
Branch: remotes/origin/d16-3-xcode11
Build date: 2019-09-17 18:39:30 UTC

=== Xamarin.Android ===

Version: 10.0.0.43 (Visual Studio Community)
Commit: xamarin-android/d16-3/8af1ca8
Android SDK: /Users/frankbuckley/Library/Developer/Xamarin/android-sdk-macosx
	Supported Android versions:
		5.0 (API level 21)
		5.1 (API level 22)
		6.0 (API level 23)
		7.0 (API level 24)
		7.1 (API level 25)
		8.0 (API level 26)
		8.1 (API level 27)

SDK Tools Version: 26.1.1
SDK Platform Tools Version: 28.0.2
SDK Build Tools Version: 28.0.3

Build Information: 
Mono: mono/mono/2019-06@7af64d1ebe9
Java.Interop: xamarin/java.interop/d16-3@5836f58
LibZipSharp: grendello/LibZipSharp/d16-3@71f4a94
LibZip: nih-at/libzip/rel-1-5-1@b95cf3f
ProGuard: xamarin/proguard/master@905836d
SQLite: xamarin/sqlite/3.27.1@8212a2d
Xamarin.Android Tools: xamarin/xamarin-android-tools/d16-3@cb41333

=== Microsoft Mobile OpenJDK ===

Java SDK: /Users/frankbuckley/Library/Developer/Xamarin/jdk/microsoft_dist_openjdk_1.8.0.25
1.8.0-25
Android Designer EPL code available here:
https://github.com/xamarin/AndroidDesigner.EPL

=== Android SDK Manager ===

Version: 1.4.0.65
Hash: c33b107
Branch: remotes/origin/d16-3
Build date: 2019-09-19 20:42:44 UTC

=== Android Device Manager ===

Version: 1.2.0.115
Hash: 724ea69
Branch: remotes/origin/d16-3
Build date: 2019-09-19 20:43:06 UTC

=== Xamarin Inspector ===

Version: 1.4.3
Hash: db27525
Branch: 1.4-release
Build date: Mon, 09 Jul 2018 21:20:18 GMT
Client compatibility: 1

=== Build Information ===

Release ID: 803001805
Git revision: df50511ccb08d4d84a53939f1d7fc0b40cbb0ee1
Build date: 2019-09-20 16:10:55+00
Build branch: release-8.3
Xamarin extensions: da8d448cd65f2cc87c5e6dc7e2c2ca7b96d20c72

=== Operating System ===

Mac OS X 10.14.6
Darwin 18.7.0 Darwin Kernel Version 18.7.0
    Tue Aug 20 16:57:14 PDT 2019
    root:xnu-4903.271.2~2/RELEASE_X86_64 x86_64