adding more links to courses and selecting which users to see

rowers/opaque.py

@@ -43,6 +43,8 @@ class OpaqueEncoder:
 
     def encode_hex(self, i):
         """Transcode an integer and return it as an 8-character hex string."""
+        if i is None:
+            return None
         return "%08x" % self.transcode(i)
 
     def encode_base64(self, i):  # pragma: no cover
@@ -51,6 +53,8 @@ class OpaqueEncoder:
 
     def decode_hex(self, s):
         """Decode an 8-character hex string, returning the original integer."""
+        if s is None:
+            return None
         return self.transcode(int(str(s), 16))
 
     def decode_base64(self, s):  # pragma: no cover