still trying to fix cache

src/licensedcode/cache.py

@@ -85,6 +85,10 @@ def load_or_build(
         # bypass build if cache exists
         if has_cache and not force:
             try:
+                # save the list of additional directories included in the cache, or None if the cache does not
+                # include any additional directories
+                with open(cached_directories_file, 'wb') as file:
+                    pickle.dump(additional_directories, file, protocol=PICKLE_PROTOCOL)
                 return load_cache_file(cache_file)
             except Exception as e:
                 # work around some rare Windows quirks
@@ -387,12 +391,13 @@ def need_cache_rebuild(additional_directories):
         # if we have cached additional directories of licenses, check if those licenses are equal to the additional
         # directories passed in
         with open(cached_directories_file, 'rb') as file:
-            cached_additional_directories = pickle.load(file)
+            # it's possible that pickle.load(file) results in None
+            cached_additional_directories = pickle.load(file) or set()
 
         # we need to rebuild the cache if the list of additional directories we passed in is not a subset of
         # the set of additional directories currently included in the index cache
-        should_rebuild_cache = additional_directories is not None and cached_additional_directories is not None\
-                               and not set(additional_directories).issubset(set(cached_additional_directories))
+        should_rebuild_cache = additional_directories is not None \
+                               and not set(additional_directories).issubset(cached_additional_directories)
     else:
         # otherwise, we don't have a file of cached directories. If there are additional directories passed in,
         # we know we need to make a new cache file.