When was the "zero admission" event in the historical imperial examination? Why is this happening?

Since Emperor Wendi of Sui Dynasty initiated the imperial examination system, the imperial examination system has undertaken the important task of selecting talents for the country with its relative fairness. However, the imperial examination is sometimes controlled by treacherous officials, and even the imperial examination has become an eternal joke. In 747, the Tang Dynasty took part in the imperial examination, but Li, the examiner, was afraid that high school candidates would influence him, so he changed the admission rate of the imperial examination to zero, which became a joke in the history of the imperial examination, and Li was reviled forever by future generations.

Li is an uneducated prime minister, narrow-minded and unwilling to recruit talents. Li himself has no talent, but as a royal family, he trusts him very much. In the later court, Li can almost have the final say. Li knows he is unworthy to be prime minister. As a result, the talents of the imperial court, such as Zhang Jiuling and many others, were squeezed out of the imperial court by Li in various ways. Knowing that he would take the exam again, Li became very worried. He doesn't want talented candidates to enter the court.

Li manipulated the results of the imperial examination and lied. Li has no way to stop the imperial examination. He thought of a way to tell Tang Xuanzong that all candidates will inevitably have some bad comments in the exam without screening. It is better to let the local authorities arrange candidates first, and then report the outstanding candidates to Shangshu Province, where they will take the exam. In those days, Fu and Gao Shi both took the exam, but Li was in the way, and people in those days were notorious. Li also made up a lie to tell the world that talented people are in the imperial court and can't recruit talents for the time being. I also listened to Li.

It can be seen from this incident that in his later years, Emperor Xuanzong of the Tang Dynasty had no intention of governing the country at all, and let Li and others run amok, which can also understand why the Anshi Rebellion happened.