Error during migration from bugzilla

[mateusz.lezuch]

There is an error while migrating from the bugzilla.
The error appears at the rewriting comments stage.  After this the migration stops. Everything is ok, but issue links are not moved.

JIM version 8.0.15 
Log:

Unexpected failure occurred. Importer will stop immediately. Data may be in an unstable state
java.lang.IllegalArgumentException: The validated object is null
at org.apache.commons.lang.Validate.notNull(Validate.java:192)
at org.apache.commons.lang.Validate.notNull(Validate.java:178)
at com.atlassian.jira.plugins.importer.imports.importer.impl.DefaultJiraDataImporter.rewriteStringWithIssueKeys(DefaultJiraDataImporter.java:241)
at com.atlassian.jira.plugins.importer.imports.importer.impl.DefaultJiraDataImporter.rewriteOldIssueKeys(DefaultJiraDataImporter.java:1399)
at com.atlassian.jira.plugins.importer.imports.importer.impl.DefaultJiraDataImporter.doImport(DefaultJiraDataImporter.java:454)
at com.atlassian.jira.plugins.importer.imports.importer.impl.ImporterCallable.call(ImporterCallable.java:26)
at com.atlassian.jira.plugins.importer.imports.importer.impl.ImporterCallable.call(ImporterCallable.java:15)
at com.atlassian.jira.task.TaskManagerImpl$TaskCallableDecorator.call(TaskManagerImpl.java:458)
at com.atlassian.jira.task.TaskManagerImpl$TaskCallableDecorator.call(TaskManagerImpl.java:426)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at com.atlassian.jira.task.ForkedThreadExecutor$ForkedRunnableDecorator.run(ForkedThreadExecutor.java:216)
at java.lang.Thread.run(Thread.java:748)
No issues need to be reindexed. 

[Andy Heinzer]

This error I believe relates to this feature request to improve the behavior of the Jira importer plugin JRASERVER-64593

In that request there are some additional warnings that are generated in the Jira logs anytime issue imported from bugzilla have issue links that Jira cannot find.  I am curious to learn if perhaps your logs also show an example like the one in that bug.