fixed; populating empty arrays works

closes #481

lib/model.js

@@ -189,8 +189,8 @@ Model.prototype.init = function (doc, query, fn) {
       } else {
         if (obj[i] && schema && populate[path]) {
           if (populate[path].sub) {
+            if (0 === obj[i].length) return next();
             var total = 0;
-
             obj[i].forEach(function (subobj) {
               for (var key in populate[path].sub) {
                 if (subobj[key]) {

lib/query.js

@@ -847,8 +847,10 @@ Query.prototype.findOne = function (callback) {
     if (!doc) return promise.complete(null);
 
     var casted = new model();
-    delete casted._doc._id; // Remove the _id, so that pre inits do not have
-                           // an _id
+
+    // Remove the _id, so that pre inits do not have one
+    delete casted._doc._id;
+
     casted.init(doc, self, function (err) {
       if (err) return promise.error(err);
       promise.complete(casted);

test/model.ref.test.js

@@ -587,6 +587,33 @@ module.exports = {
         });
       });
     });
-  }
+  },
+
+  // gh-481
+  'test populating subdocuments partially with empty array': function () {
+    var db = start()
+      , BlogPost = db.model('RefBlogPost', posts)
+      , worked = false;
+
+    var post = BlogPost.create({
+        title: 'Woot'
+      , comments: [] // EMPTY ARRAY
+    }, function (err, post) {
+      should.strictEqual(err, null);
+
+      BlogPost
+      .findById(post._id)
+      .populate('comments._creator', ['email'])
+      .run(function (err, returned) {
+        db.close();
+        worked = true;
+        should.strictEqual(err, null);
+        returned.id.should.equal(post.id);
+      });
+    });
 
+    setTimeout(function () {
+      worked.should.be.true;
+    }, 1700);
+  }
 };