best practice (and to prevent performance issue)

What are the standards when we update a record?

should we put “null” in an id field that related to another module key?

if we put " (36 spaces) " or empty (len=0) then it appears that the system interpret this as a value and try to fetch the related record.

I found out that the id that we put in could really render the system almost unsable… see
performance issue post

please confirm best practice when we do not related to an actual record… null , blank / empty ?

btw this would be applicable to uploading data as well…

Thank you