An IOException raised during analysis is swallowed by JavabinLoader, so the underlying cause is not visible in the logs, or to the client. Proposed fix is to change
throw new SolrException(SolrException.ErrorCode.SERVER_ERROR, "ERROR adding document " + document);
to
throw new SolrException(SolrException.ErrorCode.SERVER_ERROR, "ERROR adding document " + document, e);
on line 99 in JavaBinLoader.java