presto-hive/src/main/java/io/prestosql/plugin/hive/HdfsEnvironment.java/HdfsContext/toString
class HdfsContext:        @Override
        public String toString()
        {
            return toStringHelper(this)
                    .omitNullValues()
                    .add("user", identity)
                    .add("source", source.orElse(null))
                    .add("queryId", queryId.orElse(null))
                    .add("schemaName", schemaName.orElse(null))
                    .add("tableName", tableName.orElse(null))
                    .toString();
        }