Explain why _make_and() can return None

Makes ANDs between nonexistent expressions yield a nonexistent
expression.

1 files changed, 2 insertions, 1 deletions

diff --git a/kconfiglib.py b/kconfiglib.py
index 93b2279..19cf928 100644
--- a/kconfiglib.py
+++ b/kconfiglib.py
@@ -3269,7 +3269,8 @@ def _make_and(e1, e2):
     """Constructs an AND (&&) expression. Performs trivial simplification.
     Nones equate to 'y'.
 
-    Note: returns None if e1 == e2 == None."""
+    Returns None if e1 == e2 == None, so that ANDing two nonexistent
+    expressions gives a nonexistent expression."""
     if e1 is None or e1 == "y":
         return e2
     if e2 is None or e2 == "y":