Email contact form, getting a blank response

Hello.
I have had a contact form on my website running for a couple of years with no major problems. I receive emails from the contact form, so I know it’s working correctly. However, every so often, I do receive a blank response, where none of the fields have been filled in and the email subject also empty. There is also no way of identifying where the email has come from. Has anyone else had these? It wouldn’t normally bother me but I feel that I may be losing business. Is it possible that a potential customer is completing the form on my website but when it is emailed through to me it comes through blank. Like I say I do receive emails ok, just the odd couple a month.
Just for info, I do have all the fields in my website set as required.
The site is sendmeyourcv.com

Simon.

Hey @Sicherry,

given that you do have some fields marked as “required”, whatever is bypassing that is generally not a normal browser. Usually it’s spam-bots, or similar malware oriented bots that maybe attempt to discover if a form is active or perhaps pollute a honeypot, or maybe just someone experimenting with future spam. We work hard to detect bots, and to err on the safe side of letting through anything that isn’t 100% clearly a bot, in the interest of not losing valuable contacts.

Thank you Duncan for explaining it
Best regards
Simon.