ExtJS store sync send empty string instead of null

Question

I have a store with model, and this model have fields like below:

{
    name: "name",
    type: "string",
    allowNull: false,
    defaultValue: null
}

Problem is: When I update textfield with name on empty string, I send "" instead of null

textfield have allowNull: true

How to send null?

Answer 1

{name: "name", type: "string", allowNull: false, defaultValue: null}

I think allowNull should be true