public Fetcher getFetcher() {
        if (fetcherMap.size() == 0) {
            throw new IllegalArgumentException("fetchers size must == 1 for the no arg call");
        }
        if (fetcherMap.size() > 1) {
            throw new IllegalArgumentException("need to specify 'fetcherName' if > 1 fetchers are" +
                    " available");
        }
        for (Fetcher fetcher : fetcherMap.values()) {
            return fetcher;
        }
        //this should be unreachable?!
        throw new IllegalArgumentException("fetchers size must == 0");
    }
Convenience method that returns a fetcher if only one fetcher
is specified in the tika-config file.  If 0 or > 1 fetchers
are specified, this throws an IllegalArgumentException.
@return
tika-core/src/main/java/org/apache/tika/pipes/fetcher/FetcherManager.java