While previewing a report, generating a connection or running a report task,one of the error messages below may be displayed on the screen or registered in the log files:
Object Reference not set to an instance of an object ... sequence contains no elements ... unprocessed request (s)
Environment:
NPrinting September 2018 and older versions
Cause:
Invalid dimensions, measures (expressions) in Qlikview/Qlik Sense and NP filters
An unsupported or faulty Qlik Sense extension is used in the App. This must be removed or updated accordingly. See the Qlik Sense online help for version specific details.
Invalid formulas in public or private sheets
Section Access prevents access to objects owned by the NPrinting service account in the Qlik Sense app private sheets.
NOTE:
The June 2018 edition of NPrinting resolves issues with corrupted sheet or sheet objects in QlikView and Qlik Sense by ignoring them during the metadata reload.
The November 2018 edition of NPrinting resolves newly discovered issues resulting in "Object reference not set to an instance" errors.
From the Release Notes:
June 2018 Fix: Cache reload of Qlik Sense connections with invalid objects failed Jira issue ID: OP-7229 The cache reload process of Qlik Sense connections with invalid objects failed with the error: "Object reference not set to an instance of an object".? November 2018 Fix: Added a safety-check to handle "System.NullReferenceException: Object reference not set to an instance of an object" for some invalid Sense objects while reloading a Sense connection in NPrinting. JIRA ID: OP-7819
Resolution:
QlikView and Qlik Sense workarounds - 'Filter' construction and 'Expression' repair:
Correctly update sheet containing invalid objects and measures or expression so that the object measures contain valid formulas.
Make sure the field used for Filters and Report Cycling do not contain Null values by creating a column with expression isNull() in your source app objects.
Check filters to ensure they are valid and working as expected and set up correctly:
- value is: should be used with text or alphanumeric
- numeric value is: should be used with numbers or numeric values only. Make sure that the numbers seen in the date are truly numbers and not 'text'. - evaluate: should be used with using a formula to create a dynamic filter ie: Year(now()) -1
Update your dimensions and measures (expressions) such that they are valid.
- For example if you have an invalid formula in a measure, expression or dimension, this would need to be updated so that the formula is valid and the expression is "OK"
For Qlik Sense exclusively:
Remove any unneeded unpublished private sheets as they may contain objects with invalid formulas
If using Section Access, ensure no object found in a Qlik sense app private sheets are used in the report
Copy the Qlik Sense app and use the copied app for reporting purposes. The copied app does not include private sheets. Use the copied app for reporting purposes.
Remove any unsupported 'Extensions' such as On Demand extensions found in Github
NOTE: If you need to keep the private sheets, you must fix all invalid formulas in the private sheets. You must also fix any invalid formulas in your Publish Sense sheets as well. Further you can remove the sheets entirely if they are not needed.
General resolution:
To mitigate most issues regarding these errors (separate from incorrect construction of NPrinting filters), it will be necessary to upgrade to to the latest release of NPrinting to leverage fixes mentioned in this article.
