Unfilled fields

Hi
I am new to elasticsearch and I wanna ask about mapping.
If I have the following mapping :
{
"mappings":{
"properties":{
"customer_id": {"type": "integer"},
"customer_name": {"type": "text"},
"city": {"type": "keyword"}
}
}

and as I insert documents on of them did not have a city as below :
{
"customer_id": "145",
"customer_name": "charlotte"
}
My question is what value would be assigned to the "city" field? would it be "null"?
Thanks in advance

By default, no value will be assigned.

You may, however, explicitly configure a value to be indexed for the field in the field mapping. Please note, though, that this does not cause the field value to be modified in the _source of the document.