Axios: Field with undefined value set is being removed from data object

axios version 0.16.1
Environment: Mac OS Sierra, Chrome v57

I'm currently using axios.post and when I nest an object inside of the data object it appears to remove the fields inside of the nested object that have a value of undefined set.

For instance:

  update(locationId, vehicleSaleId, payload) {

    //Payload example: {billedFront: undefined}

    return axios.post('/api/vehicleSale.update', { 
        params: {locationId, vehicleSaleId}, 
        payload: payload
      })
      .then((res) => res.data);
  },

Chrome Dev Tools > Network:

{"params":{"locationId":"58e991ddb051fc0f8424552a","vehicleSaleId":"58fa4d2562fd801765652fc3"},"payload":{}}

As you can see payload is just an empty object. It should have a billedFront field that is set to undefined.