Postman GraphQL optional variables

Question

Is there a way to make a GrapqhQL variable in a Postman request "optional"? So if the value is empty/NULL the field is just not included in the request?

For example, if I have the following request:

mutation addCustomer($CustomerInput: CustomerInput!)
{
    addCustomer(
        input: $CustomerInput
    )
    {
        firstName
        lastName
    }
}

And I have the GrapqhQL variables defined as:

{
    "CustomerInput": {
        "firstName": {{firstName}},
        "lastName": {{lastName}}
    }
}

If firstName is not a required field, how can I only include it if it has a value? Right now I am getting this error:

com.fasterxml.jackson.databind.JsonMappingException: Unexpected character ('{' (code 123)): was expecting double-quote to start field name