presto-ml/src/main/java/io/prestosql/plugin/ml/LearnVarcharClassifierAggregation.java/LearnVarcharClassifierAggregation/input
class LearnVarcharClassifierAggregation:    @InputFunction
    public static void input(
            @AggregationState LearnState state,
            @SqlType(VARCHAR) Slice label,
            @SqlType("map(bigint,double)") Block features)
    {
        LearnLibSvmVarcharClassifierAggregation.input(state, label, features, Slices.utf8Slice(""));
    }