Bulk create throws invalid BulkOperationException
Bulk create throws invalid BulkOperationException

When using:
```python
es.index(doc, ELASTICSEARCH_INDEX, document_type, bulk=True,  force_insert=True)
es.flush_bulk(forced=True)
```
This was throwing a invalid BulkOperationException exception.
mavarick/pyes,jayzeng/pyes,HackLinux/pyes,haiwen/pyes,HackLinux/pyes,Fiedzia/pyes,aparo/pyes,mavarick/pyes,jayzeng/pyes,haiwen/pyes,aparo/pyes,Fiedzia/pyes,jayzeng/pyes,Fiedzia/pyes,HackLinux/pyes,aparo/pyes,haiwen/pyes,mavarick/pyes