NodeJS Error with stock Mongodb Adapter: Connection Closed By Application - node.js

Question

I'm having a weird issue with MongoDB. My database collection is closing, which I suppose is what it's supposed to do (I'm following along from the mongo boilerplate) BUT I see no reason why the docs would be null value. I've checked this every way I can think of, but I don't quite understand the cursor object.
Console.logging it seems to give me a bunch of native mongo properties ( which look like functions ie each, toArray, etc) so it seems right, but it's not a regular object with a data field that I can see.
After it hits that if block with the if(docs==null), the connection gets closed and it will not execute the each block in the else if.
Ideally if there was a way to help troubleshoot or figure out how to make this execute that would be great.
More background:
in the mongo shell I can ask for
use weather // no issues
and get the results of the data object which is 3000 records with an empty find();
var MongoClient = require('mongodb').MongoClient;
MongoClient.connect('mongodb://localhost:27017/weather', function(err, db) {
if(err){
console.log("line 7" + err);
}
var query = {};
var projection = { 'State' : 1, 'Temperature' : 1 };
var cursor = db.collection('data').find(query, projection);
console.log("cursor" + cursor); // [object Object]
var state = '';
var operator = {'$set' : {'month_high' : true } };
cursor.each(function(err, doc) {
if (err) throw err;
if (doc == null) {
console.log("docs have value:" + doc); //NULL VALUE so will close on line 23
return db.close();
} else if (doc.State !== state) {
// first record for each state is the high temp one
state = doc.State;
db.collection('data').update( {'_id':doc._id}, operator, function(err, updated) {
if (err) console.log(err);
// return db.close(); ?
});
}
});
});
{ [MongoError: Connection Closed By Application] name: 'MongoError' } //doh
{ [MongoError: Connection Closed By Application] name: 'MongoError' } //doh
{ [MongoError: Connection Closed By Application] name: 'MongoError' } //doh

Answer 1

Figuring out when to call db.close() can be a bit messy. Here it is rewritten with find().toArray() plus some logic to test when you're updating the last matched doc. This works for me.
var MongoClient = require('mongodb').MongoClient;
var assert = require('assert');
var Q = require('q');
MongoClient.connect('mongodb://localhost:27017/weather', function(err, db) {
assert.equal(null, err);
var query = {};
var projection = { 'State' : 1, 'Temperature' : 1 };
var state = '';
var operator = {'$set' : {'month_high' : true } };
var promises = [];
db.collection('data').find(query, projection).toArray(function(err, docs) {
assert.equal(null, err);
docs.forEach(function(doc, index, arr) {
var deferred = Q.defer();
promises.push(deferred.promise);
if (null !== doc && state !== doc.State) {
db.collection('data').update( {'_id':doc._id}, operator, function(err, updated) {
assert.equal(null, err);
console.log("Updated "+updated+" documents.");
deferred.resolve();
});
} else {
deferred.resolve();
}
});
Q.all(promises).done(function() {
console.log("closing");
db.close()
});
});
});
EDIT: Added Q since db.close() was still called prematurely in some cases.