fix bogus matching of child text lines against parent blank lines

diff --git a/threadview.py b/threadview.py
index 40b5841..6b93b62 100755 (executable)
--- a/threadview.py
+++ b/threadview.py
@@ -175,7 +175,7 @@ class Line:
 
     def as_hashable_inherited_line(self):
         if not self.maybe_quote:
-            return '' # will be treated as junk
+            return None # will be treated as junk; must not match anything on the other side
         stripped = self.text.strip()
         if stripped.startswith('>'):
             stripped = stripped[1:].strip()