Make title, body and mainImage properties not required and non-nullable

Author: mzdm

README.md

@@ -138,9 +138,9 @@ You should then run `flutter packages get` in your terminal so as to get the pac
 | :-------------------- | :------------- | :-------------------------------------------------------------------- | :---------------------------------------------------------------------------------------------: |
 | pageColor             | Color?          | Set color of the page.                                                |                                              Null                                               |
 | pageBackground        | Widget         | Set a widget as a background of the whole page (pageColor has priority)            |                                              Null                                               |
-| mainImage             | Image? / Widget? | Set the main image of the page.                                       |                                              Null                                               |
-| title                 | Text? / Widget?  | Set the title text of the page. If null, then the widget is omitted.                                       |                                              Null                                               |
-| body                  | Text? / Widget?  | Set the body text of the page. If null, then the widget is omitted.                                        |                                              Null                                               |
+| mainImage             | Image / Widget | Set the main image of the page. If null, then the widget is omitted. |                                              Null                                               |
+| title                 | Text / Widget  | Set the title text of the page. If null, then the widget is omitted.                                       |                                              Null                                               |
+| body                  | Text / Widget  | Set the body text of the page. If null, then the widget is omitted.                                        |                                              Null                                               |
 | iconImageAssetPath    | String?         | Set the icon image asset path that would be displayed in page bubble. |                                              Null                                               |
 | iconColor             | Color?          | Set the page bubble icon color.                                       |                                              Null                                               |
 | bubbleBackgroundColor | Color          | Set the page bubble background color.                                 |                                          Colors.white / Color(0x88FFFFFF)                                           |

lib/src/models/page_view_model.dart

@@ -8,9 +8,9 @@ class PageViewModel {
     this.iconImageAssetPath,
     this.bubbleBackgroundColor = const Color(0x88FFFFFF),
     this.iconColor,
-    required this.title,
-    required this.body,
-    required this.mainImage,
+    this.title = const SizedBox(),
+    this.body = const SizedBox(),
+    this.mainImage = const SizedBox(),
     this.bubble,
     this.textStyle,
     this.titleTextStyle = const TextStyle(color: Colors.white, fontSize: 50.0),
@@ -44,15 +44,15 @@ class PageViewModel {
   ///
   /// _Typically a [Text] widget_.
   ///
-  /// If null, then the widget is omitted.
-  final Widget? title;
+  /// Omitted by default.
+  final Widget title;
 
   /// Widget for the body.
   ///
   /// _Typically a [Text] widget_.
   ///
-  /// If null, then the widget is omitted.
-  final Widget? body;
+  /// Omitted by default.
+  final Widget body;
 
   /// Sets TextStyle for [titleTextStyle] and [bodyTextStyle].
   ///
@@ -75,9 +75,8 @@ class PageViewModel {
   ///
   /// _Typically an [Image] widget_.
   ///
-  ///
-  /// If null, then the widget is omitted.
-  final Widget? mainImage;
+  /// Omitted by default.
+  final Widget mainImage;
 
   /// Inner bubble widget.
   ///

lib/src/ui/page.dart

@@ -142,7 +142,7 @@ class _BodyPageTransform extends StatelessWidget {
         child: DefaultTextStyle.merge(
           textAlign: TextAlign.center,
           style: pageViewModel.mergedBodyTextStyle,
-          child: pageViewModel.body ?? const SizedBox(),
+          child: pageViewModel.body,
         ),
       ),
     );
@@ -173,7 +173,7 @@ class _ImagePageTransform extends StatelessWidget {
           bottom: 40.0,
         ),
         child: Container(
-          child: pageViewModel.mainImage, // Loading main
+          child: pageViewModel.mainImage,
         ),
       ),
     );
@@ -207,7 +207,7 @@ class _TitlePageTransform extends StatelessWidget {
         ),
         child: DefaultTextStyle.merge(
           style: pageViewModel.mergedTitleTextStyle,
-          child: pageViewModel.title ?? const SizedBox(),
+          child: pageViewModel.title,
         ),
       ),
     );