Preventing null exception which didn't do anything in PDF Editor Control

inabox.wpf/DynamicGrid/PDF/PDFEditorControl.xaml.cs

@@ -755,6 +755,10 @@ namespace InABox.DynamicGrid
 
         private void PdfLine_Click(object sender, RoutedEventArgs e)
         {
+            if(LineColor is null)
+            {
+                return;
+            }
             PdfViewer.LineAnnotationSettings.LineColor = (System.Windows.Media.Color)ColorConverter.ConvertFromString(LineColor);
             PdfViewer.CursorMode = PdfViewerCursorMode.SelectTool;
             PdfViewer.AnnotationMode = PdfDocumentView.PdfViewerAnnotationMode.Line;