updated project style guidelines

lib/extensions/renderNotNull.dart

@@ -1,5 +1,3 @@
 extension RenderNotNullExt<T> on T? {
-  R? wrapNullable<R>(R Function(T data) defaultValueCallback) {
-    return this != null ? defaultValueCallback(this as T) : null;
-  }
-}
+  R? wrapNullable<R>(R Function(T data) defaultValueCallback) => this != null ? defaultValueCallback(this as T) : null;
+}