anchor.diff:  
     /// Invalidate an entity in the cache.
     Future invalidate(Request key) {
  -    if (_degelate == null) {
  +    if (_delegate == null) {
         return delegateFuture.then((delegate) {
           return delegate.invalidate(key);
         });
  
positive.code: 
    /// Set an entity in the cache.
    Future set(Request key, Entity entity) {
      if (_degelate == null) {
        return delegateFuture.then((delegate) {
          return delegate.set(key, entity);
        });
  
negative.code:   
    /// Get an entity from the cache.
    Future<Entity> get(Request key) {
      if (_delegate == null) {
        return delegateFuture.then((delegate) {
          return delegate.get(key);
        });
  