private static void mergeParameters(Map<String,List<String>> source, Map<String,List<String>> destination) {
        for (Map.Entry<String, List<String>> entry : source.entrySet()) {
            List<String> destinationValues = destination.get(entry.getKey());
            if (destinationValues != null) {
                destinationValues.addAll(entry.getValue());
            } else {
                destination.put(entry.getKey(), entry.getValue());
            }
        }
    }
Merges source parameters into a destination map.

@param source containing the parameters to copy into the destination
@param destination receiver of parameters, possibly already containing data
container-core/src/main/java/com/yahoo/jdisc/http/server/jetty/FormPostRequestHandler.java