What does it mean when a researcher says The extant literature is silent on this issue?

Extant literature refers to texts that have survived from the past to the present time. Extant literature can be divided into extant originalmanuscripts, copies of original manuscripts, quotations and paraphrases of passages of non-extant texts contained in other works, translations of non-extant texts into other languages, or, more recently, photocopies or digital copies of texts.