There is nothing to create for a blank lookup itself, since it is just an empty field. What admins actually do is decide and enforce whether a given lookup is allowed to be blank. Here is how to set that policy on a single lookup field.
- Open the lookup field definition
In Setup, go to Object Manager, open the object, select Fields and Relationships, and click the lookup field you want to govern. Confirm it is a Lookup relationship and not a Master-Detail, since master-detail can never be blank.
- Set the field-level requirement
Edit the field and decide whether it is Required. Required blocks every blank save through the standard UI. Leave it optional only when an empty value is genuinely acceptable for some records.
- Choose the parent-delete behavior
On the field, set what happens when the looked-up record is deleted: Clear the value of this field (default, creates blanks), Do not allow deletion when dependencies exist, or Delete this record also for tightly coupled custom-object children.
- Add a conditional validation rule
For requirements that apply only in some cases, create a validation rule using ISBLANK on the lookup combined with the condition, for example AND(ISPICKVAL(StageName,'Closed Won'), ISBLANK(AccountId)). Write a clear error message.
- Build a blank-lookup audit report
Create a report or list view filtered to the lookup field equals empty. If a standard report type hides them, use a Custom Report Type that includes records without the related object. Review it on a schedule.
Field-level setting that forces a value on every standard UI save. All-or-nothing, with no per-context exceptions.
Default parent-delete behavior. Sets the child lookup to null when the parent is deleted, which is a common source of automatic blanks.
Parent-delete option that protects a looked-up record when other records or automation depend on the relationship.
Uses ISBLANK on the lookup to require a value only when business logic demands it, while keeping the field optional at the schema level.
- Validation rules guard the save path but data loaded through some API options or created by code that bypasses the rule can still arrive blank.
- The default Clear the value of this field deletion behavior creates blank lookups silently whenever a parent record is deleted.
- Relationship-based report types hide records with blank parent lookups, so a clean report can mask real data gaps.
- Use ISBLANK rather than ISNULL on lookups and text, since ISNULL always returns false for text fields and can mislead your logic.