presto-main/src/main/java/io/prestosql/util/JsonUtil.java/JsonUtil/isValidJsonObjectKeyType
class JsonUtil:    private static boolean isValidJsonObjectKeyType(Type type)
    {
        return type instanceof BooleanType ||
                type instanceof TinyintType ||
                type instanceof SmallintType ||
                type instanceof IntegerType ||
                type instanceof BigintType ||
                type instanceof RealType ||
                type instanceof DoubleType ||
                type instanceof DecimalType ||
                type instanceof VarcharType;
    }