Node MongoDB memory leak issue - node.js

Question

I'm writing a webservice using Node.js.
This webservice makes calls to a MongoDB and MSSQL.
For MSSQL i've use npm mssql library, for mongo i use the native npm mongodb library.
I use Q as my promise library.
I've a memory leak issue running a find over a MongoDB collection. I simply need to get elements from a connection. And eventually update the status of elements i get.
See my sample code below.
var Q = require('q');
var connection = require('..\connection.js'); //the connection module open a connection that can be used with pools.
function list(req, res) {
return Q.Promise(function(resolve, reject, notify) {
var collection = null;
var result = [];
var cursor = null;
Q.fcall(function(){}).then(function() {
collection = connection.collection(collectionName);
})
.then(function() {
cursor = collection.find({ fieldstatus : 0 });
return Q.Promise(function(resolve, reject, notify) {
Q.allSettled(cursor.each(function(err, item){
return Q.fcall(function(){
try {
if(item != null) {
result.push({
field1 : item.field1,
field2 : item.field2,
fieldstatus : item.fieldstatus
});
collection.update({_id: item._id}, {$set: {fieldstatus : 1}});
}
resolve(result);
} catch (err){
reject(err);
}
})
.fin(function() {
cursor.close();
});
}));
});
})
.then(function(ret) {
resolve(ret);
})
.fail(function(err) {
reject([ err.toString() ]);
})
.fin(function() {
result = null;
cursor = null;
collection = null;
});
})
.fail(function(err) {
throw([ err.toString() ]);
});
}
}
UPDATED : Answer 1
The code below seems to works without leak issuess.
var Q = require('q');
var connection = require('..\connection.js'); //the connection module open a connection that can be used with pools.
function list(req, res) {
return Q.Promise(function(resolve, reject, notify) {
var collection = null;
var result = [];
var cursor = null;
Q.fcall(function(){}).then(function() {
collection = connection.collection(collectionName);
})
.then(function() {
return Q.npost(
collection,
"find",
[
{ fieldstatus : 0 }
]
).then(function(ret){
return Q.npost(ret, "toArray").then(function(item){
return item;
});
})
.then(function(ret){
var result = [];
ret.forEach(function (item) {
result.push({
field1 : item.field1,
field2 : item.field2,
fieldstatus : item.fieldstatus
});
collection.update({_id: item._id}, {$set: {fieldstatus : 1}});
});
return result;
})
})
.then(function(ret) {
resolve(ret);
})
.fail(function(err) {
reject([ err.toString() ]);
})
.fin(function() {
collection = null;
});
})
.fail(function(err) {
throw([ err.toString() ]);
});
}
}