From 3ecfc67b73e472b6379ad624219493ab0993fe40 Mon Sep 17 00:00:00 2001
From: LunarLanding <4441338+LunarLanding@users.noreply.github.com>
Date: Thu, 25 Nov 2021 14:32:06 +0000
Subject: [PATCH] Allow chunks=None for dask-less lazy loading

Otherwise, the preprocess step always gets a single chunk for each variable instead of the xarray lazy accessors; dask can't change the order of slicing / computing in most cases. The default is changed to {} to maintain the default behavior.
---
 xarray/backends/api.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/xarray/backends/api.py b/xarray/backends/api.py
index 0ca82555c8f..fba5f71e3d0 100644
--- a/xarray/backends/api.py
+++ b/xarray/backends/api.py
@@ -691,7 +691,7 @@ def open_dataarray(
 
 def open_mfdataset(
     paths,
-    chunks=None,
+    chunks={},
     concat_dim=None,
     compat="no_conflicts",
     preprocess=None,
@@ -891,7 +891,7 @@ def open_mfdataset(
             "instead specify combine='nested' along with a value for `concat_dim`.",
         )
 
-    open_kwargs = dict(engine=engine, chunks=chunks or {}, **kwargs)
+    open_kwargs = dict(engine=engine, chunks=chunks, **kwargs)
 
     if parallel:
         import dask