Object reference not set to an instance of an object
  at Xamarin.Forms.Platform.MacOS.WebViewRenderer+FormsWebFrameDelegate.FinishedLoad (WebKit.WebView sender, WebKit.WebFrame forFrame) [0x00017] in <51ba4bc9dbf845159a2acda030a83ce4>:0 
  at (wrapper managed-to-native) AppKit.NSApplication.NSApplicationMain(int,string[])
  at AppKit.NSApplication.Main (System.String[] args) [0x00040] in /Library/Frameworks/Xamarin.Mac.framework/Versions/4.8.0.22/src/Xamarin.Mac/AppKit/NSApplication.cs:100 
  at LogotecAppStudio.macOS.MainClass.Main (System.String[] args) [0x00017] in /Users/kulikow/Desktop/Projects/AppStudio2018/LogotecAppStudio/LogotecAppStudio.macOS/Main.cs:11

using System;
using System.Threading.Tasks;
using Foundation;
using WebKit;
using Xamarin.Forms;
using Xamarin.Forms.Platform.MacOS;
using WebView = Xamarin.Forms.WebView;

[assembly: ExportRenderer(typeof(WebView), typeof(LogotecAppStudio.macOS.Renderers.LasWebViewRenderer))]
namespace LogotecAppStudio.macOS.Renderers
{
	public class LasWebViewRenderer : WebViewRenderer
	{
		protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.WebView> e)
		{
			base.OnElementChanged(e);

			if (Control != null &&
				Control.FrameLoadDelegate is FormsWebFrameDelegate == false &&
				Control.FrameLoadDelegate is WebKit.WebFrameLoadDelegate wfd)
			{
				Control.FrameLoadDelegate = new FormsWebFrameDelegate(this, wfd);
			}
		}

		internal class FormsWebFrameDelegate : WebKit.WebFrameLoadDelegate
		{
			WebViewRenderer _renderer;
			WebKit.WebFrameLoadDelegate _wfd;

			internal FormsWebFrameDelegate(WebViewRenderer renderer, WebKit.WebFrameLoadDelegate wfd)
			{
				_renderer = renderer;
				_wfd = wfd;
			}

			public override void FinishedLoad(WebKit.WebView sender, WebFrame forFrame)
			{
				try
				{
					if (_renderer.Control == null) return;
					_wfd.FinishedLoad(sender, forFrame);
				}
				catch
				{
					// ignore
				}
			}

			public override void FailedLoadWithError(WebKit.WebView sender, NSError error, WebFrame forFrame)
			{
				try
				{
					if (_renderer.Control == null) return;
					_wfd.FailedLoadWithError(sender, error, forFrame);
				}
				catch
				{
					// ignore
				}
			}
		}
	}
}