Daily Chinese Idiom Guessing Game
Fictitious or nonexistent; something invented or imaginary.
子虚并非真实；乌有哪有。指假设的、不存在的、不真实的事情。
汉·司马相如著《子虚赋》楚使子虚使于齐，王悉发车骑，与使者出畋。畋罢，子虚过奼乌有先生，亡是公存焉。”
The story about the treasure is just a sub-xu-wu-you tale.