Re: Should we consider empty fields as NULL values when dealing with string columns ?

The rest of your post was answered, but I'll add the following. You should
set your error_reporting level higher, so you are warned if you are
referencing an unassigned variable. There is something wrong with your
script if you aren't validating data.
When using script languages (like PHP) if by mistake the variable is not
defined such insert is possible (let's say we have a variable $col1_value
and after a long day of work we make a mistake and write it $col_value).