Is there a way to set default empty string "" parameter in swagger - django rest framework?

Question

I use drf-yasg to generate swagger documentation for my api.

I would want set empty "" string instead "string" as default. How can I do?

properties = {
        'type_operator': openapi.Schema(type=openapi.TYPE_INTEGER,  description="L'operatore di insieme AND(0) OR(1)"),
        'column_to_hide': openapi.Schema(type=openapi.TYPE_STRING,description="L'elenco di colonne da nascondere separato da virgola")
    }