title: JSON formatting? Bad request during PUT to set asana custom fields
body: <p>I'm trying to remove the value of a custom field on an asana task via a PUT request. </p>
  
  <p>Based on the original json data I sent over to create the task with a custom field value and <a href="https://asana.com/developers/api-reference/tasks#setting_custom_field_values" rel="nofollow noreferrer">the documentation here</a> this is my best guess for how this should look:</p>
  
  <pre><code>let data = {custom_fields: { ASANA_CUSTOM_FIELD_ID_NUMBER: null }}; //struggling here
  updateTask(ASANA_TASK_ID_NUMBER, data);
  
  
  function updateTask(id, data) {
    return put(`https://app.asana.com/api/1.0/tasks/${ASANA_TASK_ID_NUMBER}`, data);
  }
  
  function put(url, data) {
    return makeRequest({
      "url": url,
      "headers": {"Authorization": "Bearer " + accessCode()},
      "type": "PUT",
      "data": data
    })
  }
  </code></pre>
  
  <p>But I get the error:</p>
  
  <pre><code>status:400 Bad request 
  custom_fields: Value cannot be an array: []
  </code></pre>
  
  <p>Which seems verbose enough to solve except I've tried every format i can come up with and I've had no luck working it out. I know that the put function works fine for updating other fields for a task and I see the same error with an actual number other than null. </p>