put = async (doc) => {
    const key = doc[indexBy]

    if (!key) { throw new Error(`The provided document doesn't contain field '${indexBy}'`) }

    return addOperation({ op: 'PUT', key, value: doc })
  }
Stores a document to the store.
@function
@param {Object} doc An object representing a key/value list of fields.
@return {string} The hash of the new oplog entry.
@memberof module:Databases.Databases-Documents
@instance