SNOW-CAD Practice Question: Automating application logic with business rules and scripts
Exhibit
2023-10-01 12:34:56 Error: Script error: Cannot read property 'sys_id' of null Script: Business Rule "Update Related Records" on Incident table Line: 15
Refer to the exhibit. Which scenario most likely caused this error?
⚠ Common exam trap
ServiceNow often tests the distinction between 'current' and 'previous' objects in Business Rules, and the trap here is that candidates may not realize 'previous' is null for new records, leading them to incorrectly assume the error is about a missing field or inactive rule.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The Business Rule uses 'previous.sys_id' but the record is new.
When a Business Rule runs on 'insert' or 'update' and references 'previous.sys_id', the 'previous' object is null for new records (since there is no prior version). This causes a 'Cannot read property 'sys_id' of null' error. The error occurs specifically because the script attempts to access a property on an undefined object.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The Business Rule runs on delete and 'current' is null.
Why it's wrong here
Current is never null on delete.
- ✗
The Business Rule tries to access a field that doesn't exist.
Why it's wrong here
Would give 'undefined' not 'null' error.
- ✓
The Business Rule uses 'previous.sys_id' but the record is new.
Why this is correct
On insert, previous is null.
- ✗
The Business Rule is not active.
Why it's wrong here
Inactive rule would not produce error.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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