function setBufferProp(src, dst, propName, def) {
        if(!dst) return;
        if (src && dst) {
            var buf = src[propName];
            if (buf && typeof Buffer.isBuffer(buf)) {
                dst[propName] = Buffer.from(buf);
            }
        } else {
            if(def != undefined) dst[propName] = def;
        }
    }
Helper function for copying the MQTT v5 buffer type properties
NOTE: if src[propName] is not a buffer, dst[propName] will NOT be assigned a value (unless def is set)
@param {object} src Source object containing properties
@param {object} dst Destination object to set/add properties
@param {string} propName The property name to set in the Destination object
@param {boolean} [def] An optional default to set in the destination object if prop is NOT present in the Source object