R missing bib key in citation() output

I am using citation() to automatically get the bib entries for R packages. However, its output does not have a key.

Example:

utils:::print.bibentry(citation(), style = "Bibtex")

Output:

@Manual{,
  title = {R: A Language and Environment for Statistical Computing},
  author = {{R Core Team}},
  organization = {R Foundation for Statistical Computing},
  address = {Vienna, Austria},
  year = {2017},
  url = {https://www.R-project.org/},
}

I would like something like this:

@Manual{mykey999,
  title = {R: A Language and Environment for Statistical Computing},
  author = {{R Core Team}},
  organization = {R Foundation for Statistical Computing},
  address = {Vienna, Austria},
  year = {2017},
  url = {https://www.R-project.org/},
}

I've tried the same command with the "key" argument but it changes nothing:

utils:::print.bibentry(citation(), style = "Bibtex", key= "mykey0")

Any idea?