Fix removal of ignored assignment files

Author: shreve

nbgrader/coursedir.py

@@ -361,7 +361,10 @@ def find_assignments(self,
         # Locate all matching directories using a glob
         dirs = list(
             filter(
-                lambda p: p.is_dir() and not is_ignored(p.relative_to(self.root), self.ignore),
+                lambda p: (
+                    p.is_dir()
+                    and not is_ignored(str(p.relative_to(self.root)), self.ignore)
+                ),
                 Path(self.root).glob(self.directory_structure.format(**kwargs))
             )
         )

nbgrader/utils.py

@@ -272,11 +272,14 @@ def self_owned(path):
     return get_osusername() == find_owner(os.path.abspath(path))
 
 
-def is_ignored(filename: str, ignore_globs: List[str]) -> bool:
+def is_ignored(filename: str, ignore_globs: List[str] = None) -> bool:
     """Determines whether a filename should be ignored, based on whether it
     matches any file glob in the given list. Note that this only matches on the
     base filename itself, not the full path."""
 
+    if ignore_globs is None:
+        return False
+
     basename = os.path.basename(filename)
     for expr in ignore_globs:
         if fnmatch.fnmatch(basename, expr):