From c53dc205ed0c1911295a2f741781920b840808d7 Mon Sep 17 00:00:00 2001
From: Tianshu Wang <wang@tianshu.me>
Date: Fri, 11 Nov 2022 19:21:22 +0800
Subject: [PATCH] Make sure save_dir can be empty str (#15638)

---
 src/pytorch_lightning/callbacks/model_checkpoint.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/pytorch_lightning/callbacks/model_checkpoint.py b/src/pytorch_lightning/callbacks/model_checkpoint.py
index 1403b754be..85c6e1aac6 100644
--- a/src/pytorch_lightning/callbacks/model_checkpoint.py
+++ b/src/pytorch_lightning/callbacks/model_checkpoint.py
@@ -584,7 +584,10 @@ class ModelCheckpoint(Checkpoint):
             return self.dirpath
 
         if len(trainer.loggers) > 0:
-            save_dir = trainer.loggers[0].save_dir or trainer.default_root_dir
+            if trainer.loggers[0].save_dir is not None:
+                save_dir = trainer.loggers[0].save_dir
+            else:
+                save_dir = trainer.default_root_dir
             name = trainer.loggers[0].name
             version = trainer.loggers[0].version
             version = version if isinstance(version, str) else f"version_{version}"