Added asserts.
diff --git a/packages/flutter_tools/lib/src/build_info.dart b/packages/flutter_tools/lib/src/build_info.dart
index c599cba..3664066 100644
--- a/packages/flutter_tools/lib/src/build_info.dart
+++ b/packages/flutter_tools/lib/src/build_info.dart
@@ -99,6 +99,7 @@
     case 'linux-x64':
       return TargetPlatform.linux_x64;
   }
+  assert(platform != null);
   return null;
 }