Looks like allowEmptyValue not implemented. The goal is to produce a query parameter ?param1 without any value and the '=' sign. Tried the following

{
        in: "query",
        name: "param1",
        type: "string",
        required: false,
        allowEmptyValue : true
}

with different type, but can't send ?param1 in the URL. The closest I can get is ?param1=true using:

{
        in: "query",
        name: "param1",
        type: "string",
        required: false,
        enum : ["true"]
}

Ideally, if allowEmptyValue = true, then ui presents a checkbox: when checked send ?param1, else just do not include the parameter.