Failed to execute OnFrame callback

As far as I know, the plugin is working but I'm seeing this in the console:

Failed to execute OnFrame callback (Object reference not set to an instance of an object.)
   at void Oxide.Plugins.SignManager.AddSign(BaseEntity e)+() => { } in /home/container/carbon/plugins/SignManager.cs:line 104
   at void Carbon.Managers.CarbonProcessor.Update() in /home/runner/work/Carbon/Carbon/src/Carbon/src/Processors/CarbonProcessor.cs:line 63

I know that ChatGPT can be wrong, but I uploaded the error, my data file and your response and this is what it concluded:
 

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The file itself does not appear malformed.

I do not see obvious literal null entries.

The risky part is the many empty arrays [], which may represent signs/users/entities with no actual sign data saved.

InsCRC: 0 may also be suspicious, depending on how the plugin uses it.

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your visible data file does not look broken because of []; the plugin bug is that it assumes the Signs[id] value is never null.

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Empty arrays are not the direct cause.

The plugin is vulnerable if any storedData.Signs[someId] value is null, or if the data deserialized oddly for one entry.

The dev was basically right that a null-check is needed, but the code should guard both the dictionary and the list value.

I don't really understand a lot of that, but maybe that will help?