need to get null value rows data

I am working on an expression rule. In that rule, I need to get rows with null values as output. I am providing some map inputs like {username: test, fname: test1, lname: test2, email: test@gmail.com, username: test, fname: test1, lname: test2, email: ""}. I want to get the output as: {username: test, fname: test1, lname: test2, email: ""}.  I am getting only null.However, I am unable to get the exact output. Can anyone help me out?.Thanks for your help in adavnce

a!localVariables(
  local!users: a!forEach(
    items: ri!users,
    expression: a!map(
      username: fv!item.username,
      firstname: fv!item.firstname,
      lastname: fv!item.lastname,
      email: fv!item.email
    )
  ),
  local!nullValueUsers: a!forEach(
    items: local!users,
    expression: if(
      or(
        isnull(fv!item.username),
        isnull(fv!item.firstname),
        isnull(fv!item.lastname),
        isnull(fv!item.email)
      ),
      fv!item,
      null
    )
  ),
  local!nulldataValueUsers: reject(fn!isnull, local!nullValueUsers),
  local!nulldataValueUsers
)

###rule input datatype- Map

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