Laminas\Diactoros\UploadedFile could not be converted to string

Hi everybody, have you ever encoutered with “Object of class Laminas\Diactoros\UploadedFile could not be converted to string” error, when you do not attach file into a form, i.e. you send a filled form without attached file?

In fact, in my form, I have three various input fileds for submitting files. Everything works perfectly, when I fill the form and attach all files. When I do not attach files at all or attach only 1 or 2 files, I am getting the error above.

Is there any way to enable empty attachments for Laminas\Diactoros\UploadedFile ?

Thank you very much!

My controller code is here: