Fix cached None support in FlakeCacheEntry

Previously, you could cache None values; however,
insertion wasn't idempotent/identical reinsertion
would lead to errors due to missing None checks.

pkgs/clan-cli/clan_cli/flake.py

@@ -246,6 +246,12 @@ class FlakeCacheEntry:
                 if self.value != value:
                     msg = "value mismatch in cache, something is fishy"
                     raise TypeError(msg)
+
+        elif value is None:
+            if self.value is not None:
+                msg = "value mismatch in cache, something is fishy"
+                raise TypeError(msg)
+
         else:
             msg = f"Cannot insert value of type {type(value)} into cache"
             raise TypeError(msg)