Mongodb grouping statement by custom file - mongodb

Question

I want to retrieve data from mongodb, grouping and summing for a custom field based in a db field which can exist or not but I don't have the result I expect because I there is no data ggrupation (see attached file)enter image description here. The mongo statement is:
aggregate({
$match: {
owner: 'W99999',
creation_date: {
$gte: 1530748800,
$lte: 1531292133
}
},
$project: {
isWarm: {
$cond: [{
$not: ["$referral"] }, 1, 0 ]
},
isCold: {
$cond: [{
$not: ["$referral"] }, 0, 1 ]
},
daysBefore: {
$subtract: [6, {
$trunc: {
$divide: [{
$subtract: ['$creation_date', 1530748800]
}, 86400]
}
}]
}
},
$group: {
_id: {
isWarm: { $sum: "$isWarm" },
isCold: { $sum: "$isCold" },
daysBefore: '$daysBefore'
}
})
I think the problem is the "isWarm" and "isCold" condition for creating them. Thank you in advance.
UPDATE 05/07/2018.
Schema (trunked for security reasons):
{
"_id": "1",
"creation_date":"1515780901",
"referral: //This field is optional.
{
some_data: { }
},
more_data: { }
}
Result expected:
{ [
{ isCold: 3, isWarm: 2, daysBefore: 0 },
{ isCold: 2, isWarm: 5, daysBefore: 1 },
{ isCold: 5, isWarm: 0, daysBefore: 2 },
{ isCold: 1, isWarm: 2, daysBefore: 3 },
{ isCold: 1, isWarm: 1, daysBefore: 4 },
{ isCold: 1, isWarm: 0, daysBefore: 5 },
{ isCold: 0, isWarm: 0, daysBefore: 6 }
] }
I would like to have the object even if there is no documents to count (e.g. last line of the result).
RESOLVED: I need to test with real data.
I think I have a solution:
[{ $project: {
_id: 0,
daysBefore: {
$subtract: [6, {
$trunc: {
$divide: [{
$subtract: ['$creation_date', 1530748800] }, 86400]
}
}]
},
isWarm: {$cond: [{ $gte: ['$referral', null]}, 1, 0]},
isCold: {$cond: [{ $gte: ['$referral', null]}, 0, 1]}} },
{
$group:
{
_id: { creation_date: '$daysBefore' },
isWarm: { $sum: '$isWarm' },
isCold: { $sum: '$isCold' }
}
}]