---
 src/whoosh/matching/mcore.py |    3 +++
 1 file changed, 3 insertions(+)

--- a/src/whoosh/matching/mcore.py
+++ b/src/whoosh/matching/mcore.py
@@ -379,6 +379,9 @@ class NullMatcherClass(Matcher):
     def __repr__(self):
         return "<NullMatcher>"
 
+    def __hash__(self):
+        return hash((self.is_active(), tuple(self.all_ids())))
+
     def supports_block_quality(self):
         return True