Verifying empty email

I have OTP set up for email on a contact form. If I leave the email field empty, when I click the “Click here to verify email” button it shows a success message along the lines of “A One Time Passcode (OTP) has been sent to .”. This is using up my email transactions credit even though the email field is empty.

I suspect there are bots or users automatically clicking this button and chewing through my credit.

Can the verification form show an error if the email field is empty?