We need more information to investigate this issue. Please create a case task with customer support team and our team will further investigate this issue.
Root cause:A Reference field used in the lookup was configured to reference the wrong table. When the Partial Preview API attempted to perform the reference lookup, it was unable to fetch the target data, and the internal query object remained uninitialized. That led to the exception:
There was an error with the partial preview API. Transformation failed: Cannot invoke "com.glide.db.meta.Query.addQuery(com.glide.util.IQueryCondition)" because "this.fQuery" is null
Fix:Correct the Reference field configuration (Dictionary entry) so theReferencepoints to the correct table.
We ran into the exact same issue while integrating Cisco Collector with ServiceNow using IntegrationHub ETL.
Root Cause
The problem occurredafter deploying the ETL configuration from one instance to another.
When moving ETL configurations via Update Sets,not all ETL-related records are consistently captured, especially if changes were made directly in the ETL (for example adding or removing fields in the transform). In our case, some related records under the Robust Transform Engine were missing in the target instance.
Because of that mismatch, the ETL Transform Map preview failed with:
"There was an error with the partial preview API."
And Step 2 –Prepare Source Data for Mapping– showed no data.
What to Check
Open theData Sourcefrom which the ETL is selected.
Open theRobust Transform.
Open theTransformer Definition.
In theRelated List, check theRobust Transform Engine Entityrecords.
Compare the number of records between:
Source instance (where it works)
Target instance (where the error occurs)
In our case, the record counts were different between the two instances.
Resolution
We manually recreated/synchronized the missingRobust Transform Engine Entityrecords in the target instance so that both instances matched.
After correcting the difference, the ETL Transform Map preview worked correctly and Step 2 populated the source data as expected.
Important Note
In our experience,ServiceNow Update Sets do not always capture ETL changes completely, especially when modifying fields directly inside the ETL configuration (like adding/removing fields). These related Robust Transform Engine records can sometimes be missed.
If you encounter this partial preview API error after deployment, definitely compare the Robust Transform Engine Entity records between instances.
