code: function get_related_in_payload(collection, payload) {
    // If there's nothing to filter, just exit with nothing.
    if (!payload) return []
  
    // Get the keys that are associations in the collection.
    const related_in_collection = new Set(get_related_columns(collection))
  
    // Filter the payload based on the collection's associations.
    return Object.keys(payload).filter(key => related_in_collection.has(key))
  }
docs: Get the(any) related key names in the payload.
  
  @param  {Waterline.Collection} collection to get related attributes in.
  @param  {Object} payload to get related keys from.
  @return {Array<string>} Array of related attributes in the payload.