title: Sequelize defaultValue not getting set
body: <p>Here is my model for a recipe table.  I am using mysql as the database, and the sequelize module.  If I leave the title, prep_time, or cook_time blank in the form it seems to skip the validation of allowNull and defaultValue and attempts to enter a '' (blank string) into the database.  Is there something I am doing wrong?  </p>
  
  <pre><code>module.exports = function(sequelize, DataTypes) {
      return sequelize.define('recipe', {
          title: {
              type: DataTypes.STRING,
              allowNull: false
          },
          description: {
              type: DataTypes.TEXT
          },
          ingredients: {
              type: DataTypes.TEXT
          },
          instructions: {
              type: DataTypes.TEXT
          },
          yield: {
              type: DataTypes.STRING
          },
          prep_time: {
              type: DataTypes.INTEGER,
              allowNull: false,
              defaultValue: '0'
          },
          cook_time: {
              type: DataTypes.INTEGER,
              allowNull: false,
              defaultValue: '0'
          },
          image: {
              type: DataTypes.STRING
          }
      });
  };
  </code></pre>