From 86e7b1981f063a04a8b3cdbdeaa395280c86dc2b Mon Sep 17 00:00:00 2001
From: Alinson S Xavier <axavier@anl.gov>
Date: Thu, 24 Sep 2020 15:05:54 -0500
Subject: [PATCH] Revert changes to default variable category

---
 miplearn/instance.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/miplearn/instance.py b/miplearn/instance.py
index 1313f97..10157b3 100644
--- a/miplearn/instance.py
+++ b/miplearn/instance.py
@@ -78,9 +78,9 @@ class Instance(ABC):
         model to predict the values of both variables. If the returned category is None, ML
         models will ignore the variable.
 
-        By default, returns None.
+        By default, returns "default".
         """
-        return None
+        return "default"
 
     def has_static_lazy_constraints(self):
         return False