CallScriptMethod Sierra 10.12 issue

After the call

this.WebBrowser.WindowScriptObject.CallWebScriptMethod (script, new NSObject[]{});

my application is crashing with exception

System.NullReferenceException: Object reference not set to an instance of an object
  at (wrapper managed-to-native) MonoMac.AppKit.NSApplication:NSApplicationMain (int,string[])
  at MonoMac.AppKit.NSApplication.Main (System.String[] args) [0x00041] in /Users/builder/data/lanes/3508/c1e5fa01/source/xamarin-macios/src/AppKit/NSApplication.cs:94 
  at Safelog.Program.Main (System.String[] args) [0x00054] in /Users/robert/Downloads/Safelog_Win/Safelog.Mac/Program.cs:40

That code works fine in previous versions of macOS