Here is how the data is structured in my firebase firestore

users: {
xyz: {
 profile: {
    email: "[email protected]"
}
},
pqr:  {
profile: {
email: "[email protected]"
}
}

but as email is optional in my system so i want get only the users that have a not null email and a non blank email. How do i query those?

As a context, I am coming from realtime database World where i was forced to store the email address directly under user id node rather a level down. Do i have to do the same thing in firestore as well?