Fix #21

Author: nekocode

lib/src/settings/flutter.dart

@@ -4,8 +4,12 @@ import 'package:yaml/yaml.dart';
 class Flutter {
   Flutter(YamlMap flutterMap) {
     if (flutterMap != null) {
-      assets = FlutterAssets(safeCast<YamlList>(flutterMap['assets']));
-      fonts = FlutterFonts(safeCast<YamlList>(flutterMap['fonts']));
+      if (flutterMap.containsKey('assets')) {
+        assets = FlutterAssets(safeCast<YamlList>(flutterMap['assets']));
+      }
+      if (flutterMap.containsKey('fonts')) {
+        fonts = FlutterFonts(safeCast<YamlList>(flutterMap['fonts']));
+      }
     }
   }
 

lib/src/settings/flutter_gen.dart

@@ -8,10 +8,14 @@ class FlutterGen {
   FlutterGen(YamlMap flutterGenMap) {
     if (flutterGenMap != null) {
       _output = safeCast<String>(flutterGenMap['output']);
-      integrations = FlutterGenIntegrations(
+      if (flutterGenMap.containsKey('integrations')) {
+        integrations = FlutterGenIntegrations(
           safeCast<YamlMap>(flutterGenMap['integrations']));
+      }
       _lineLength = safeCast<int>(flutterGenMap['lineLength']);
-      colors = FlutterGenColors(safeCast<YamlMap>(flutterGenMap['colors']));
+      if (flutterGenMap.containsKey('colors')) {
+        colors = FlutterGenColors(safeCast<YamlMap>(flutterGenMap['colors']));
+      }
     }
   }