presto-main/src/main/java/io/prestosql/operator/aggregation/histogram/Histogram.java/Histogram/Histogram
class Histogram:    public Histogram(HistogramGroupImplementation groupMode)
    {
        super(
                new FunctionMetadata(
                        new Signature(
                                NAME,
                                ImmutableList.of(comparableTypeParameter("K")),
                                ImmutableList.of(),
                                mapType(new TypeSignature("K"), BIGINT.getTypeSignature()),
                                ImmutableList.of(new TypeSignature("K")),
                                false),
                        true,
                        ImmutableList.of(new FunctionArgumentDefinition(false)),
                        false,
                        true,
                        "Count the number of times each value occurs",
                        AGGREGATE),
                true,
                false);
        this.groupMode = groupMode;
    }