Return None for SyncCheckpoint.read() when src is empty

Signed-off-by: Andrew Dye <[email protected]>

flytekit/core/checkpointer.py

@@ -146,7 +146,9 @@ def read(self) -> typing.Optional[bytes]:
         if p is None:
             return None
         files = list(p.iterdir())
-        if len(files) == 0 or len(files) > 1:
+        if len(files) == 0:
+            return None
+        if len(files) > 1:
             raise ValueError(f"Expected exactly one checkpoint - found {len(files)}")
         f = files[0]
         return f.read_bytes()

tests/flytekit/unit/core/test_checkpoint.py

@@ -83,6 +83,16 @@ def test_sync_checkpoint_restore_default_path(tmpdir):
     assert cp.restore() == cp._prev_download_path
 
 
+def test_sync_checkpoint_read_empty_dir(tmpdir):
+    td_path = Path(tmpdir)
+    dest = td_path.joinpath("dest")
+    dest.mkdir()
+    src = td_path.joinpath("src")
+    src.mkdir()
+    cp = SyncCheckpoint(checkpoint_dest=str(dest), checkpoint_src=str(src))
+    assert cp.read() is None
+
+
 def test_sync_checkpoint_read_multiple_files(tmpdir):
     """
     Read can only work with one file.