private Fetcher getFetcher(FetchEmitTuple t) {
        try {
            return fetcherManager.getFetcher(t.getFetchKey().getFetcherName());
        } catch (IllegalArgumentException e) {
            String noFetcherMsg = getNoFetcherMsg(t.getFetchKey().getFetcherName());
            LOG.warn(noFetcherMsg);
            write(STATUS.FETCHER_NOT_FOUND, noFetcherMsg);
            return null;
        } catch (IOException | TikaException e) {
            LOG.warn("Couldn't initialize fetcher for fetch id '" + t.getId() + "'", e);
            write(STATUS.FETCHER_INITIALIZATION_EXCEPTION, ExceptionUtils.getStackTrace(e));
            return null;
        }
    }
returns stack trace if there was a container exception or empty string
if there was no stacktrace

@param t
@param metadataList
@return
tika-core/src/main/java/org/apache/tika/pipes/PipesServer.java