fix more runtime issues

com.unity.uiwidgets/Runtime/cupertino/app.cs

             Dictionary<LogicalKeySet, Intent> shortcuts = null,
             Dictionary<LocalKey, ActionFactory> actions = null
         ) : base(key: key) {
-            D.assert(routes != null);
-            D.assert(navigatorObservers != null);
-            D.assert(showPerformanceOverlay != null);
-            D.assert(checkerboardRasterCacheImages != null);
-            D.assert(checkerboardOffscreenLayers != null);
-            D.assert(showSemanticsDebugger != null);
-            D.assert(debugShowCheckedModeBanner != null);
 
             supportedLocales = supportedLocales ?? new List<Locale> {new Locale("en", "US")};
             this.navigatorKey = navigatorKey;

com.unity.uiwidgets/Runtime/widgets/basic.cs

             this.softWrap = softWrap;
             this.overflow = overflow;
             this.textScaleFactor = textScaleFactor;
-            this.maxLines = maxLines ?? 0;
+            this.maxLines = maxLines;
             this.locale = locale;
             this.strutStyle = strutStyle;
             this.textWidthBasis = textWidthBasis;
         public readonly  bool softWrap;
         public readonly  TextOverflow overflow;
         public readonly  float textScaleFactor;
-        public readonly  int maxLines;
+        public readonly  int? maxLines;
         public readonly  Locale locale;
         public readonly  StrutStyle strutStyle;
         public readonly  TextWidthBasis textWidthBasis;

com.unity.uiwidgets/Runtime/widgets/framework.cs

 
         public T dependOnInheritedWidgetOfExactType<T>(object aspect = null) where T : InheritedWidget {
             D.assert(_debugCheckStateIsActiveForAncestorLookup());
-            InheritedElement ancestor = _inheritedWidgets == null ? null : _inheritedWidgets[typeof(T)];
+            InheritedElement ancestor = _inheritedWidgets == null ? null : _inheritedWidgets.getOrDefault(typeof(T));
             
             if (ancestor != null) {
                 D.assert(ancestor is InheritedElement);

com.unity.uiwidgets/Runtime/widgets/text.cs

         public override void debugFillProperties(DiagnosticPropertiesBuilder properties) {
             base.debugFillProperties(properties);
             style?.debugFillProperties(properties);
-            properties.add(new EnumProperty<TextAlign>("textAlign", textAlign.Value, defaultValue: null));
+            properties.add(new EnumProperty<TextAlign?>("textAlign", textAlign, defaultValue: null));
             properties.add(new FlagProperty("softWrap", value: softWrap, ifTrue: "wrapping at box width", ifFalse: "no wrapping except at line break characters", showName: true));
             properties.add(new EnumProperty<TextOverflow>("overflow", overflow, defaultValue: null));
             properties.add(new IntProperty("maxLines", maxLines, defaultValue: null));