mongo has null code example
Example 1: mongodb exists and not null
db.collection1.find({ 'fieldname1' : { $exists: true, $ne: null } });
Example 2: mongodb query missing field
db.inventory.find( { item: null } )
db.collection1.find({ 'fieldname1' : { $exists: true, $ne: null } });
db.inventory.find( { item: null } )