add null check for text in TextLayoutBackend

the text should never be null, because the toolkits require
a string value, when drawing. Otherwise WPF and MAC
throw a NullReferenceException and Gtk prints
a warning to the console (Pango-CRITICAL).

1 files changed, 2 insertions, 2 deletions

diff --git a/Xwt.WPF/Xwt.WPFBackend/TextLayoutBackendHandler.cs b/Xwt.WPF/Xwt.WPFBackend/TextLayoutBackendHandler.cs
index ca422b9d..229ee2a9 100644
--- a/Xwt.WPF/Xwt.WPFBackend/TextLayoutBackendHandler.cs
+++ b/Xwt.WPF/Xwt.WPFBackend/TextLayoutBackendHandler.cs
@@ -112,7 +112,7 @@ namespace Xwt.WPFBackend
 		SolidColorBrush brush = System.Windows.Media.Brushes.Black;
 		double width;
 		double height;
-		string text = null;
+		string text = String.Empty;
 		Xwt.Drawing.TextTrimming? textTrimming;
 		bool needsRebuild;
 
@@ -160,7 +160,7 @@ namespace Xwt.WPFBackend
 		{
 			if (this.text != text)
 			{
-				this.text = text;
+				this.text = text ?? String.Empty;
 				needsRebuild = true;
 			}
 		}