[TYPO3-mvc] TYPO3 6.2.: Upload in form creates empty file references

[Natalia Postnikova]

Hi,

I tried to implement the file upload in frontend in my own extension 
(FAL). There is an example extension by Helmut Hummel which almost works:
http://typo3.helmut-hummel.de/post/85015526410/file-upload-using-extbase-and-fal-in-typo3-6-2

When there is already an image uploaded and assigned to the entry and I 
submit the form once again without a new image, a new entry is created 
in the sys_file_reference table. That means that by submitting the form 
without changes I get new entries in sys_file_reference to the same image.

Does anyone have an idea how to solve this? Is there a working example 
how to upload images?

Thank you,
Natalia