presto-ml/src/main/java/io/prestosql/plugin/ml/type/ClassifierType.java/ClassifierType/ClassifierType
class ClassifierType:    public ClassifierType(Type type)
    {
        super(new TypeSignature(ClassifierParametricType.NAME, TypeSignatureParameter.typeParameter(type.getTypeSignature())));
        checkArgument(type.isComparable(), "type must be comparable");
        labelType = type;
    }