fixed $inc not updating values of 0

lib/resources/collection.js

@@ -128,7 +128,6 @@ Collection.prototype.sanitize = function (body) {
  */
 
 Collection.prototype.handle = function (ctx) {
-
   // set id one wasnt provided in the query
   ctx.query.id = ctx.query.id || this.parseId(ctx) || (ctx.body && ctx.body.id);
 
@@ -509,6 +508,7 @@ Collection.prototype.execCommands = function (type, obj, commands) {
             var val = commands[key][k];
 
             if(k === '$inc') {
+              if(!obj[key]) obj[key] = 0;
               obj[key] += val;
             }
             if(k === '$push') {