Merge fields issue

Merge fields issue

For the tags $[FNAME]$ $[LNAME]$, they work well if both columns are filled with our client's first and last names. However, if a client chose not to give his last name, the automatic process doesn't leave the field blank, as it should. Instead, in the email, it leaves the $[LNAME]$. So now we have clients receiving an email with

"Hello, John $[LNAME]$ ,"

How is this possible? Is there a way to avoid this? We would prefer the result to be

"Hello, John ,"

Thank you.