如何确保为空表单字段发送null而不是0

I have a table with columns that allow null values and has a default null value. On update, if the field is empty (not data inserted) my script inserts 0 instead of null. I have gone through similar questions as mine and i have tried the advice given but am still not able to fix my issue. Here's my codeI have a table with columns that allow null val