What does it mean if there is no version model?
Is it normal? I expect the money year after the words "MacBook Air" similar to this.
I would like to buy this particular Mac, should I worry about it?
It's not normal, but it might be nothing. The next reinstall of the OS or an update might populate that field for you.
As far as I can tell, some time during installation the OS checks with Apple and downloads a localized string to represent the hardware. Since you're not US - perhaps there was an outage or an error localizing the string.
Unless there's other cause for concern - you could try reinstalling the OS - choose US location and language to see if that's related. Try looking up the serial number using the answer of the last link (The Stack Overflow question).
In your case, that's reported as a MacBook Air (13-inch, Early 2015) and you could change the language code to get a localized version.
Some other reading on serial numbers and the OS: