Did you miss the question? It asks how to set a column to NULL with placeholders, not set it to the default. NULL may or may not be the default for a column.
Comment on Re^4: MySQL: placeholders and NULL values
which I have shown to be untrue. Doing that WILL set it to NULL.
Jeff japhy Pinyan,
P.L., P.M., P.O.D, X.S.:
Perl,
regex,
and perlhacker How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart