Fixed the type map for QString to properly handle null.

Signed-off-by: Dimitar Dobrev <dpldobrev@protonmail.com>

Author: ddobrev

QtSharp.CLI/Program.cs

@@ -95,8 +95,21 @@ public static int Main(string[] args)
                     dependencies[libFile] = Enumerable.Empty<string>();
                 }
             }
-            var modules = new List<string> { "Qt5Core", "Qt5Gui", "Qt5Widgets", "Qt5Xml", "Qt5Designer", "Qt5Network", "Qt5Qml",
-                "Qt5Nfc", "Qt5OpenGL", "Qt5ScriptTools", "Qt5Sensors", "Qt5SerialPort"};
+            var modules = new List<string>
+                          {
+                              "Qt5Core",
+                              "Qt5Gui",
+                              "Qt5Widgets",
+                              "Qt5Xml",
+                              "Qt5Designer",
+                              "Qt5Network",
+                              "Qt5Qml",
+                              "Qt5Nfc",
+                              "Qt5OpenGL",
+                              "Qt5ScriptTools",
+                              "Qt5Sensors",
+                              "Qt5SerialPort"
+                          };
             if (debug)
             {
                 for (var i = 0; i < modules.Count; i++)

QtSharp/QString.cs

@@ -20,9 +20,9 @@ public override string CSharpSignature(CSharpTypePrinterContext ctx)
 
         public override void CSharpMarshalToNative(MarshalContext ctx)
         {
-            ctx.SupportBefore.WriteLine("var __stringPtr{0} = (ushort*) Marshal.StringToHGlobalUni({1}).ToPointer();",
+            ctx.SupportBefore.WriteLine("var __stringPtr{0} = ReferenceEquals({1}, null) ? null : (ushort*) Marshal.StringToHGlobalUni({1}).ToPointer();",
                                         ctx.ParameterIndex, ctx.Parameter.Name);
-            ctx.SupportBefore.WriteLine("var __qstring{0} = QtCore.QString.FromUtf16(ref *__stringPtr{0}, {1}.Length);",
+            ctx.SupportBefore.WriteLine("var __qstring{0} = __stringPtr{0} == null ? null : QtCore.QString.FromUtf16(ref *__stringPtr{0}, {1}.Length);",
                                         ctx.ParameterIndex, ctx.Parameter.Name);
             var type = ctx.Parameter.Type.Desugar();
             if (type.IsAddress())