fixed minor bug when handling unassigned associations

src/SequelizeTable.js

@@ -274,6 +274,9 @@ SequelizeTable = function(sequelize, tableName, attributes) {
       })
       
       table.prototype[assocName] = function(callback) {
+        if((this[_table.identifier] == null)||(isNaN(this[_table.identifier])))
+          callback([])
+        else
           _table.find(this[_table.identifier], callback)
       }