diff --git a/benchexec/tablegenerator/statistics.py b/benchexec/tablegenerator/statistics.py
index <HASH>..<HASH> 100644
--- a/benchexec/tablegenerator/statistics.py
+++ b/benchexec/tablegenerator/statistics.py
@@ -37,9 +37,10 @@ class ColumnStatistics(object):
     )
 
     def __getattr__(self, name):
+        # This is called for fields that have not been set previously, default is None
         if name in ColumnStatistics._fields:
-            return None
-        return super().__getattr__(name)
+            return None  # noqa: R501 specifying None explicitly is clearer
+        raise AttributeError("can't get attribute " + name)
 
     def __setattr__(self, name, value):
         if name in ColumnStatistics._fields:
Improve implementation of __getattr__

object does not actually define __getattr__, so the previous
implementation would raise AttributeError implicitly,
which happens to be exactly what we need in this case.
However, raising it explicitly is better understandable.

Found with pytype