Does elasticsearch consider empty string as null?

I would like to know if elasticsearch considers empty string as null value, but based on my mapping shown below, I don't see that it is doing that. How can I make elasticsearch consider empty string as a null and index using the value provided by null_value. My mapping is shown below:

{
    "mapping": {
        "my_typee": {
            "properties": {
                "autoRank": {
                    "type": "integer",
                    "null_value": 0,
                    "store": true,
                    "index": "analyzed"
                }
            }
        }
    }
}

Thanks in advance.