UntypedMetric pruneData() {
        UntypedMetric pruned = new UntypedMetric(null);
        pruned.outputFormat = this.outputFormat;
        pruned.current = this.current;
        return pruned;
    }
A gauge or a counter or... who knows? The class for storing a metric when the
metric has not been declared.

@author Steinar Knutsen
container-core/src/main/java/com/yahoo/metrics/simple/UntypedMetric.java