[Bug-1398]Error generating json value

Hello,

I’m relativelly new working with Ignition, done some testing of the tool, using maker for personal use, and seriously considering aquiring the tool professionally. On that sense, I’ve been doing some proof of concepts using perspective module, and I came across an error that is spamming the logs:

jsonvalues 29Jan2021 09:29:46 Error generating json value
java.lang.NullPointerException: null

I’ve looked around the forum, but I can’t seem to pinpoint the origin of the problem. I see no problems while navigating the different pages, and everything seems to be working, including the few scripts I’ve done. But the log messages keep coming…

Any ideas?

Thank you in advance,
Bruno Nunes

We need quite a bit more information than your screenshot provides. Is it the Gateway log where are you seeing this error? Could you include more in the screenshot? Anything with line numbers or a description of what portion of the application is throwing this error would be very helpful. Your Ignition version would also be helpful.

If the project is small enough, you could send an export of the project to me through direct message (click my username and then select “Message”) and I could look to see where the issue is.

The logs are in “Diagnostics - Logs” and that information seems to be all that I can retrieve from the log.
Version 8.1.1 (b2020120808)
I attach the log file exportIgnition-SRVAVSIOT0001_Ignition_logs_20210129-1642.zip (1.3 MB)

If you still consider it useful, i’ll certainly forward you the project export.

Again, thanks a lot for the reply.

Bruno Nunes

@bruno.nunes Yes, the project would be a lot easier to diagnose.

By setting the jsonvalues logger to trace we were able to locate the origin of the error, though the error should still not be encountered. I’ve opened an internal ticket to address the issue, and hopefully improve that logging to be more helpful.

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Hi @bruno.nunes -

I believe this is fixed in 8.1.2. Could you try upgrading and let us know if the issue persists? If it does persist, could you add -XX:-OmitStackTraceInFastThrow to your wrapper.java.additional parameters in ignition.conf, restart the gateway, and report the full stack trace that you see?

Thank you,

As explained to @cmallonee via private message, I deleted the motor instances, added the history enabled to freq and torq to the UDT itself, and reinstanciated the 13 motors and got not more errors since. I sent him some extra information about the project.

I will upgrade nonetheless, and thank you very much for the attention, and will report if something happens!

Thank you.

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@cmallonee I am encountering this error in an 8.1.1 project that is on a gateway that is not readily able to be upgraded to 8.1.2 or restarted to look at the stack traces. Do you have any suggestions for things I could try to fix this?

We were never able to ascertain the origin of the issue - one of the user’s tags had become “orphaned” in some way but was still registered and trying to report history/changes.

Helpful steps:
In the Gateway > Status Logs page, we set the logging level of the tags.execution.nodes.ext.jsonvalues logger to “trace”.
This resulted in the logs giving us some information about what tag was actually having an issue.
The user investigated the tags declared in the trace logging.
The user then elected to “rebuild” the tags/UDTs in that directory in order to repair any orphaned definitions, and the error ceased following their repair.

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It looks like the following steps can replicate this issue, which has been marked as resolved in 8.1.2:

  1. Create a UDT and an instance.
  2. In a perspective view add a component and bind directly to the UDT instance so that JSON is returned.
  3. Rename or delete the instance so the component binding is now invalid.
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I have a flex repeater with instances that display information about a UDT tag. The instances are created dynamically based on the results of a tag folder browse. There is a possibility that I renamed one of the UDT tags in the folder at some point, but I can’t recall. I changed the logging levels as you suggested, then used the tag names that came in with the error to delete and remake the problem UDT instances. This seems to have fixed it. Thank you @cmallonee

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