You either have to
1) update the database to set a default value for nameProduct, or set it to allow NULL.
2) update your insert and update server behavior to set a value if blank to "blank" instead of "default", since there is no default set in the database.
The line of code in question would be:
$UpdateQuery->bindColumn("nameProduct", "s", "".((isset($_POST["txtNameProduct"]))?$_POST["txtNameProduct"]:"") ."", "WA_DEFAULT");
it would become:
$UpdateQuery->bindColumn("nameProduct", "s", "".((isset($_POST["txtNameProduct"]))?$_POST["txtNameProduct"]:"") ."", "WA_BLANK");