don't omit null for associated foreign keys

lib/associations/has-many-single-linked.js

@@ -22,7 +22,7 @@ module.exports = (function() {
 
     // clear the old associations
     oldAssociations.forEach(function(associatedObject) {
-      associatedObject[self.__factory.identifier] = options.omitNull ? '' : null
+      associatedObject[self.__factory.identifier] = /*options.omitNull ? '' :*/ null
       chainer.add(associatedObject.save())
     })
 

lib/associations/has-one.js

@@ -54,7 +54,7 @@ module.exports = (function() {
       return new Utils.CustomEventEmitter(function(emitter) {
         obj[self.accessors.get]().success(function(oldObj) {
           if(oldObj) {
-            oldObj[self.identifier] = options.omitNull ? '' : null;
+            oldObj[self.identifier] = /*options.omitNull ? '' :*/ null;
             oldObj.save()
           }
 

lib/utils.js

@@ -119,7 +119,7 @@ var Utils = module.exports = {
       var _hash = {}
 
       Utils._.each(hash, function(val, key) {
-        if(val !== null && val !== undefined) {
+        if (key.match(/Id$/) || ((val !== null) && (val !== undefined))) {
           _hash[key] = val;
         }
       })

spec/associations/has-many.spec.js

@@ -154,7 +154,7 @@ describe('HasMany', function() {
     })
 
     it("clears associations when passing null to the set-method with omitNull set to true", function(done) {
-      this.sequelize.options.omitNull = true;
+      this.sequelize.options.omitNull = true
 
       var User = this.sequelize.define('User', { username: Sequelize.STRING })
         , Task = this.sequelize.define('Task', { title: Sequelize.STRING })