dart fix

ltx_flutter/lib/constants/colors.dart

@@ -18,7 +18,7 @@ enum CategoryColor {
   final String hex;
 
   name() {
-    return this.toString().split('.').last;
+    return toString().split('.').last;
   }
 
   backgroundColor() {

ltx_flutter/lib/pages/categories_page.dart

@@ -48,6 +48,7 @@ class _CategoriesPageState extends State<CategoriesPage> {
               }
               return CategoryRow(category: category);
             }
+            return null;
           },
         );
       }),
@@ -79,26 +80,26 @@ class CategoryRow extends StatelessWidget {
         children: [
           Container(
             constraints: BoxConstraints(maxHeight: 80, maxWidth: 70),
-            color: category?.backgroundColor,
+            color: category.backgroundColor,
             child: SizedBox.expand(
               child: Center(
                   child: Text(
                       style: TextStyle(
                         fontWeight: FontWeight.bold,
-                        color: category?.foregroundColor,
+                        color: category.foregroundColor,
                         fontSize: 18,
                       ),
-                      category!.number.toString())),
+                      category.number.toString())),
             ),
           ),
           Expanded(
             child: Padding(
-              padding: EdgeInsets.only(left: category!.leftPadding()),
+              padding: EdgeInsets.only(left: category.leftPadding()),
               child: Text(
                 style: TextStyle(
                   fontSize: 17,
                 ),
-                category!.name,
+                category.name,
               ),
             ),
           ),
@@ -110,7 +111,7 @@ class CategoryRow extends StatelessWidget {
                   fontSize: 13,
                   color: Colors.white38,
                 ),
-                "${category?.description}",
+                "${category.description}",
               ),
             ),
           ),