Unknown stats.json causes IllegalArgumentException when receiving the Gogs webhook

03:20:22.786 [http-nio-8080-exec-7] INFO  o.g.s.c.GitRepositoryWebhookController - Receive webhook from upstream 'dbk-ddi32' with correlationId 86669360-5789-444d-8e35-dfabfa066120
03:20:22.786 [http-nio-8080-exec-7] INFO  o.g.s.c.GitRepositoryWebhookController - Process pipeline task EXTEND_STUDY_DESCRIPTION
03:20:22.786 [q-1] DEBUG org.gesis.commons.git.JGitRepository - git pull master in /stardat-converter/working-directory/dbk-ddi32 from ssh://git@svko-docker2.gesis.intra:3022/gesis/dbk-ddi32.git
03:20:23.001 [q-1] DEBUG org.gesis.commons.git.JGitRepository - git pull master in /stardat-converter/working-directory/dbk-ddi32-extended from ssh://git@svko-docker2.gesis.intra:3022/gesis/dbk-ddi32-extended.git
03:20:23.105 [q-1] DEBUG o.g.s.c.GitRepositoryWebhookController - Commit faa2bfb1370d76ea7b8b136ecbf7f6f1a676491e
 - Timestamp: 2021-10-03T03:20:06Z
 - Added documents: []
 - Modified documents: [svko-dbk02_gesis_intra-DBK/stats.json, svko-dbk02_gesis_intra-ED/stats.json]
 - Removed documents: []
03:20:23.237 [q-1] ERROR o.g.s.c.GitRepositoryWebhookController - null
java.lang.IllegalArgumentException: null
        at java.base/java.util.concurrent.ThreadPoolExecutor.<init>(Unknown Source)
        at java.base/java.util.concurrent.ThreadPoolExecutor.<init>(Unknown Source)
        at java.base/java.util.concurrent.Executors.newFixedThreadPool(Unknown Source)
        at org.gesis.stardat.converter.TaskExecutorFactory.runParallelAndWait(TaskExecutorFactory.java:56)
        at org.gesis.stardat.converter.GitRepositoryWebhookController.lambda$processExtendStudyDescription$6(GitRepositoryWebhookController.java:156)
        at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(Unknown Source)
        at java.base/java.util.stream.SortedOps$SizedRefSortingSink.end(Unknown Source)
        at java.base/java.util.stream.AbstractPipeline.copyInto(Unknown Source)
        at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(Unknown Source)
        at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(Unknown Source)
        at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(Unknown Source)
        at java.base/java.util.stream.AbstractPipeline.evaluate(Unknown Source)
        at java.base/java.util.stream.ReferencePipeline.forEach(Unknown Source)
        at org.gesis.stardat.converter.GitRepositoryWebhookController.processExtendStudyDescription(GitRepositoryWebhookController.java:141)
        at org.gesis.stardat.converter.GitRepositoryWebhookController.lambda$receiveUpstreamWebhook$0(GitRepositoryWebhookController.java:108)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.base/java.lang.Thread.run(Unknown Source)
13:18:10.752 [http-nio-8080-exec-5] INFO  o.g.s.c.GitRepositoryWebhookController - Receive webhook from upstream 'dbk-ddi32' with correlationId e0e7aaed-ef16-4698-b4dd-ba62ae83c81c
13:18:10.753 [http-nio-8080-exec-5] INFO  o.g.s.c.GitRepositoryWebhookController - Process pipeline task EXTEND_STUDY_DESCRIPTION
13:18:10.753 [q-1] DEBUG org.gesis.commons.git.JGitRepository - git pull master in /stardat-converter/working-directory/dbk-ddi32 from ssh://git@svko-docker2.gesis.intra:3022/gesis/dbk-ddi32.git
13:18:10.976 [q-1] DEBUG org.gesis.commons.git.JGitRepository - git pull master in /stardat-converter/working-directory/dbk-ddi32-extended from ssh://git@svko-docker2.gesis.intra:3022/gesis/dbk-ddi32-extended.git
13:18:11.058 [q-1] DEBUG o.g.s.c.GitRepositoryWebhookController - Commit 80958a0d2d1993f8685316b9ebeb500b7a05eb0e
 - Timestamp: 2021-10-03T13:18:00Z
 - Added documents: []
 - Modified documents: [svko-dbk02_gesis_intra-DBK/stats.json, svko-dbk02_gesis_intra-ED/stats.json]
 - Removed documents: []
13:18:11.185 [q-1] ERROR o.g.s.c.GitRepositoryWebhookController - null
java.lang.IllegalArgumentException: null
        at java.base/java.util.concurrent.ThreadPoolExecutor.<init>(Unknown Source)
        at java.base/java.util.concurrent.ThreadPoolExecutor.<init>(Unknown Source)
        at java.base/java.util.concurrent.Executors.newFixedThreadPool(Unknown Source)
        at org.gesis.stardat.converter.TaskExecutorFactory.runParallelAndWait(TaskExecutorFactory.java:56)
        at org.gesis.stardat.converter.GitRepositoryWebhookController.lambda$processExtendStudyDescription$6(GitRepositoryWebhookController.java:156)
        at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(Unknown Source)
        at java.base/java.util.stream.SortedOps$SizedRefSortingSink.end(Unknown Source)
        at java.base/java.util.stream.AbstractPipeline.copyInto(Unknown Source)
        at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(Unknown Source)
        at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(Unknown Source)
        at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(Unknown Source)
        at java.base/java.util.stream.AbstractPipeline.evaluate(Unknown Source)
        at java.base/java.util.stream.ReferencePipeline.forEach(Unknown Source)
        at org.gesis.stardat.converter.GitRepositoryWebhookController.processExtendStudyDescription(GitRepositoryWebhookController.java:141)
        at org.gesis.stardat.converter.GitRepositoryWebhookController.lambda$receiveUpstreamWebhook$0(GitRepositoryWebhookController.java:108)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.base/java.lang.Thread.run(Unknown Source)
03:20:21.968 [http-nio-8080-exec-7] INFO  o.g.s.c.GitRepositoryWebhookController - Receive webhook from upstream 'dbk-ddi32' with correlationId 7ddfe82e-a1e6-461d-9511-c616c1d4a0b5
03:20:21.968 [http-nio-8080-exec-7] INFO  o.g.s.c.GitRepositoryWebhookController - Process pipeline task EXTEND_STUDY_DESCRIPTION