code: @SuppressWarnings("unchecked")
      public <A, B> Maybe<B> get(TypeSafeKey<A, B> key) {
          return maybe((A) table.get(key)).fmap(view(key));
      }
docs: Retrieve the value at this key.
  
  @param key the key
  @param <A> the value type
  @param <B> the value type
  @return Maybe the value at this key