presto-main/src/main/java/io/prestosql/execution/buffer/OutputBuffers.java/OutputBuffers/checkHasBuffer
class OutputBuffers:    private void checkHasBuffer(OutputBufferId bufferId, int partition)
    {
        checkArgument(
                Objects.equals(buffers.get(bufferId), partition),
                "OutputBuffers already contains task %s, but partition is set to %s not %s",
                bufferId,
                buffers.get(bufferId),
                partition);
    }