protected static String joinCreators(List<String> creators) {
        if (creators == null || creators.size() == 0) {
            return "";
        }
        if (creators.size() == 1) {
            return creators.get(0);
        }
        StringJoiner stringJoiner = new StringJoiner(", ");
        for (String s : creators) {
            stringJoiner.add(s);
        }
        return stringJoiner.toString();
    }
Tries to extract Dublin Core schema from XMP.  If XMPMetadata is null
or if the DC schema is null, this will return without throwing an exception.

@param xmpMetadata XMPMetadata to process
@param metadata    Tika's metadata to write to
tika-parsers/tika-parsers-standard/tika-parsers-standard-modules/tika-parser-xmp-commons/src/main/java/org/apache/tika/parser/xmp/JempboxExtractor.java