Temporary fix for that weird crash

src/Gtk/Perspex.Cairo/Media/FormattedTextImpl.cs

@@ -25,7 +25,7 @@ namespace Perspex.Cairo.Media
             FontWeight fontWeight)
         {
             Contract.Requires<NullReferenceException>(context != null);
-
+            Contract.Requires<NullReferenceException> (text != null);
             Layout = new Pango.Layout(context);
             _text = text;
             Layout.SetText(text);

src/Perspex.SceneGraph/Media/FormattedText.cs

@@ -29,6 +29,9 @@ namespace Perspex.Media
             TextAlignment textAlignment,
             FontWeight fontWeight)
         {
+            //TODO: Find out why it was null in the first place. Demo project - AvalonStudio
+            //https://github.com/VitalElement/AvalonStudio/commit/787fb9396feb74e6ca6bd4e08436269a349df9c6
+            text = text ?? "";
             Text = text;
             FontFamilyName = fontFamilyName;
             FontSize = fontSize;