Noticed that if you enter "Null" as a last name, you register that a last name was entered but store the actual value as a Null type. Like the name : "John Null", cannot be saved in Marketo. I am trying to figure out how that would be possible and whether there is something exploitable here.
Marketo reserves the four-letter string "NULL", case-insensitive, as if it were the unquoted keyword NULL. This is known behavior.
"Exploitable", not really, just frustrating under clear circumstances.
Note all form-encoded values are character streams, so given Marketo form logic *something* had to be reserved as the "emptifier" value.