presto-main/src/main/java/io/prestosql/sql/planner/optimizations/BeginTableWrite.java/BeginTableWrite/addMaterializedHandle
class BeginTableWrite:        public void addMaterializedHandle(WriterTarget handle, WriterTarget materializedHandle)
        {
            checkState(!this.handle.isPresent(), "can only have one WriterTarget in a subtree");
            this.handle = Optional.of(handle);
            this.materializedHandle = Optional.of(materializedHandle);
        }