code: public JsonDocument insert(String documentId, String json) {
          return this.bucket.insert(JsonDocument.create(documentId, JsonObject.fromJson(json)));
      }
docs: Inserts a {@link JsonDocument} if it does not exist already.
  
  @param documentId the unique ID of the document
  @param json       the JSON String representing the document to store
  @return the newly created {@link JsonDocument}
  @see Bucket#insert(Document)