TypeError with Upload

Hello! I use Vaadin 13 in my java project, and I want to upload a file to my application, and then I want to use data from this file in my programm. I added FileBuffer, Upload and upload.addSucceededListener to my code, but when I tried to upload a file, I receive a message: “TypeError: Cannot read property ‘status’ of null”. What can I do to fix it? I am a beginner in Vaadin, so please give me a detailed answer.