Fixed NullReferenceException in AbstractBuildOptions.InitTargetFramework.

src/Main/Base/Project/Src/Gui/Dialogs/OptionPanels/ProjectOptions/AbstractBuildOptions.cs

@@ -243,8 +243,11 @@ namespace ICSharpCode.SharpDevelop.Gui.OptionPanels
 			ComboBox targetFrameworkComboBox = ControlDictionary["targetFrameworkComboBox"] as ComboBox;
 			if (targetFrameworkComboBox != null) {
 				targetFrameworkComboBox.Enabled = false;
-				targetFrameworkComboBox.Items.Add(((IUpgradableProject)project).CurrentTargetFramework.DisplayName);
-				targetFrameworkComboBox.SelectedIndex = 0;
+				TargetFramework fx = ((IUpgradableProject)project).CurrentTargetFramework;
+				if (fx != null) {
+					targetFrameworkComboBox.Items.Add(fx.DisplayName);
+					targetFrameworkComboBox.SelectedIndex = 0;
+				}
 			}
 		}
 	}