ListViewRenderer dataSource is null

I've been trying to copy the iOS CostomRenderer from IncredibleWeb/Xamarin-Forms-Chat-Client.
The Exception cause is a nullReferenceException, but i've traced the issue to this line:

table.Source = new ListViewDataSourceWrapper(this.GetFieldValue<UITableViewSource>(typeof(ListViewRenderer), "dataSource"));

where GetFieldValue looks like this:

public static T GetFieldValue<T>(this object @this, Type type, string name) {
            var field = type.GetField(name, BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.GetField);
            return (T)field.GetValue(@this);
        }

the field ist what is null and causes the exception to be thrown.

Just before the point of failure, the field also gives this error:

Unable to cast object of type 'System.RuntimeType' to type 'Mono.Debugger.Soft.TypeMirror'.

Googleing this error has yielded no enlightenment.
Values before Error

I am completely at a loss here and don't know which parts of the code might be helpful to figuer this out.!

Any help would be greatly appreciated!