Fix empty file checksum

Reference: https://github.com/aboutcode-org/scancode-toolkit/pull/4149/files#r1983173751
Signed-off-by: Ayan Sinha Mahapatra <[email protected]>

Author: AyanSinhaMahapatra

src/commoncode/hash.py

@@ -217,6 +217,8 @@ def checksum(location, name, base64=False):
     """
     Return a checksum from the content of the file at ``location`` using the ``name`` checksum
     algorithm. The checksum is a string as a hexdigest or is base64-encoded is ``base64`` is True.
+
+    Return None if ``location`` is not a file or an empty file.
     """
     if not filetype.is_file(location):
         return
@@ -290,6 +292,9 @@ def multi_checksums(location, checksum_names=("md5", "sha1", "sha256", "sha512",
     if not filetype.is_file(location):
         return {name: None for name in checksum_names}
     file_size = get_file_size(location)
+    if file_size == 0:
+        return {name: None for name in checksum_names}
+
     hashers = {
         name: get_hasher_instance_by_name(name=name, total_length=file_size)
         for name in checksum_names

tests/data/hash/empty

@@ -194,3 +194,8 @@ def test_checksum_from_chunks_from_stream_is_same_as_plain(self):
         for _ in range(100):
             result2.update(chunk)
         assert result1 == result2.hexdigest()
+
+    def test_checksum_empty_file(self):
+        test_file = self.get_test_loc("hash/empty")
+        checksums = multi_checksums(location=test_file, checksum_names=("sha1",))
+        assert checksums == {"sha1": None}