Adding Null type values
Pro:

• Allows null or any other name for it to be used in such cases

  [[author]]
  email = null
  name = "Lorem Ipsum"
  bookname = "dolor sit amet"
  website = "https:///www.lipsum.com/"
  
  [[author]]
  email = "[email protected]"
  name = "Eiusmod Tempor"
  bookname = "Iusto Odio"
  website = null

Cons:

• it might not look so human freindly but null can be replaced as none, nothing, etc.