mongoose find field not exists code example

Example 1: mongodb exists and not null

db.collection1.find({ 'fieldname1' : { $exists: true, $ne: null } });

Example 2: Mongodb Mongoose : Find all docs where field doesn't exists, plus if field exists apply condition

db.stackoverflow.find({
  $or: [
    { howmuch: { $exists:false } },
    { howmuch:5 }
  ]})