replace empty container with collection operators

Author: prakhar1989

flutter-app/lib/label_samples_grid.dart

@@ -45,22 +45,22 @@ class ListLabelSamples extends StatelessWidget {
           child: new Hero(
             tag: AppBar,
             child: new AppBar(
-                leading: const BackButton(),
-                title: new Text('${labelName.toUpperCase()}'),
-                actions: !isOwner
-                    ? [Container()]
-                    : [
-                        IconButton(
-                          icon: Icon(Icons.delete_forever),
-                          onPressed: () {
-                            Firestore.instance
-                                .collection('labels')
-                                .document(labelKey)
-                                .delete();
-                            Navigator.pop(context);
-                          },
-                        ),
-                      ]),
+              leading: const BackButton(),
+              title: new Text('${labelName.toUpperCase()}'),
+              actions: [
+                if (isOwner)
+                  IconButton(
+                    icon: Icon(Icons.delete_forever),
+                    onPressed: () {
+                      Firestore.instance
+                          .collection('labels')
+                          .document(labelKey)
+                          .delete();
+                      Navigator.pop(context);
+                    },
+                  ),
+              ],
+            ),
           ),
           preferredSize: new AppBar().preferredSize,
         ),
@@ -227,16 +227,16 @@ class ImageViewerDialog extends StatelessWidget {
       backgroundColor: Colors.black,
       contentPadding: EdgeInsets.all(0),
       children: <Widget>[
-        new Container(
-          decoration: BoxDecoration(color: Colors.black),
+        Container(
+          decoration: const BoxDecoration(color: Colors.black),
           child: imageUrl.isNotEmpty
               ? FadeInImage.memoryNetwork(
                   fadeInDuration: const Duration(milliseconds: 200),
                   placeholder: kTransparentImage,
                   image: imageUrl,
                   fit: BoxFit.fitWidth,
                 )
-              : Icon(Icons.image, size: 200, color: Colors.black12),
+              : const Icon(Icons.image, size: 200, color: Colors.black12),
         ),
       ],
     );

flutter-app/lib/labelscreen.dart

@@ -293,7 +293,7 @@ class _ListLabelsScreenState extends State<ListLabelsScreen> {
                         builder: (BuildContext context) => LabelsHelpDialog());
                   },
                 ),
-                isOwner ? buildPopupMenu() : Container(),
+                if (isOwner) buildPopupMenu(),
               ],
             ),
           ),
@@ -495,22 +495,20 @@ class LabelEntry extends StatelessWidget {
                 crossAxisAlignment: CrossAxisAlignment.center,
                 children: <Widget>[
                   new Text(labelName),
-                  _canEdit(model)
-                      ? new Row(
-                          children: [
-                            Chip(
-                              avatar: CircleAvatar(
-                                backgroundColor: Colors.grey.shade800,
-                                child: Text('$totalImages'),
-                              ),
-                              label:
-                                  Text(totalImages == 1 ? 'image' : 'images'),
-                              backgroundColor: Colors.white24,
-                            ),
-                            const Icon(Icons.navigate_next),
-                          ],
-                        )
-                      : Container(),
+                  if (_canEdit(model))
+                    new Row(
+                      children: [
+                        Chip(
+                          avatar: CircleAvatar(
+                            backgroundColor: Colors.grey.shade800,
+                            child: Text('$totalImages'),
+                          ),
+                          label: Text(totalImages == 1 ? 'image' : 'images'),
+                          backgroundColor: Colors.white24,
+                        ),
+                        const Icon(Icons.navigate_next),
+                      ],
+                    ),
                 ],
               )),
         ),

flutter-app/lib/main.dart

@@ -112,18 +112,18 @@ class _MyHomePageState extends State<MyHomePage> {
       appBar: new AppBar(
         title: new Text("Datasets"),
         actions: <Widget>[
-          model.isLoggedIn()
-              ? Container()
-              : IconButton(
-                  onPressed: () {
-                    model
-                        .beginSignIn()
-                        .then((user) => model.setLoggedInUser(user))
-                        .catchError((e) => print(e));
-                  },
-                  icon: Icon(
-                    Icons.person_outline,
-                  )),
+          if (!model.isLoggedIn())
+            IconButton(
+              onPressed: () {
+                model
+                    .beginSignIn()
+                    .then((user) => model.setLoggedInUser(user))
+                    .catchError((e) => print(e));
+              },
+              icon: Icon(
+                Icons.person_outline,
+              ),
+            ),
           model.isLoggedIn()
               ? PopupMenuButton<MainAction>(
                   onSelected: (MainAction action) {