Exception: System.NullReferenceException in Editor.ChemDoodleWeb800

[MikeWilliams-UK]

Some users are seeing this Exception

Editor.ChemDoodleWeb800.WpfChemDoodle.SwitchToMulti_OnClick()

Exception	
System.NullReferenceException: Object reference not set to an instance of an object.
 at Chem4Word.Model.Converters.Json.JSONConverter.AddMolecule(Object data, Model newModel) in C:\Dev\vsts\chem4word\Version3\src\Chemistry\Chem4Word.Model\Converters\Json\JSONConverter.cs:line 171
 at Chem4Word.Model.Converters.Json.JSONConverter.Import(Object data) in C:\Dev\vsts\chem4word\Version3\src\Chemistry\Chem4Word.Model\Converters\Json\JSONConverter.cs:line 160
 at Chem4Word.Editor.ChemDoodleWeb800.WpfChemDoodle.SwitchToMulti_OnClick(Object sender, RoutedEventArgs e) in C:\Dev\vsts\chem4word\Version3\src\PlugIns\Editors\ChemDoodleWeb.800\WpfChemDoodle.xaml.cs:line 422

in JSONConverter.cs at line 171 change

foreach (AtomJSON a in data.a)
{
}

To

if (data.a != null)
{
  foreach (AtomJSON a in data.a)
  {
  }
}