Bug: ABC fails with ERRO[0042] elastic: Error 400 (Bad Request): request body is required

When parsing thousands of documents, ABC intermittently throws the following error and stops the indexing process.

```
ERRO[0042] elastic: Error 400 (Bad Request): request body is required [type=parse_exception] version=5 writer=elasticsearch
```

We've seen this issue in the importer GUI and were able to fix it with a retry request. The same could work here.

- ABC version is `0.6.6`.