I want to correct the datatypes of all of my input field values ?

I WANT TO WRITE ALL THE FIELD VALUES THAT CONTAINS Blank Values INTO NULL 
I used these expression for to write specific one field = field ${str:length(record:value('/VENDOR_NAME_ALT')) != 0 ? record:value('/VENDOR_NAME_ALT') : 'null'}

but i want to use all  fields  that contains blank values means feed with  NULL . 
any other processor can replace these scenario