From: Wez Furlong <wez@fb.com>
Date: Mon, 8 Jan 2018 21:57:43 -0800
Subject: fix art.t test failure on alpine linux

Summary:
Looks like we end up with root_ holding a nullptr after
the associated test is finished.  This only seems to be a problem
in practice on Alpine linux's musl libc based environment, and
only when built with `-O2`.  Not sure if this is a c++ standard
library implementation issue or a compiler optimization, or a
combination of both of those things.

Guard against that with a simple nullptr check.

Refs https://github.com/facebook/watchman/issues/546

Reviewed By: simpkins

Differential Revision: D6681244

fbshipit-source-id: f119b3552c0aeedc325fa83c71b12745536b1dac
(cherry picked from commit e77eb9597c4c094a0b0bbeef0b957b49b40b87eb)

Origin: upstream v2020.05.11.00
Bug: https://github.com/facebook/watchman/issues/546
---
 thirdparty/libart/src/art-inl.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/thirdparty/libart/src/art-inl.h b/thirdparty/libart/src/art-inl.h
index fce055b..acc7cd6 100644
--- a/thirdparty/libart/src/art-inl.h
+++ b/thirdparty/libart/src/art-inl.h
@@ -760,7 +760,7 @@ art_tree<ValueType, KeyType>::Node::maximum() const {
 template <typename ValueType, typename KeyType>
 typename art_tree<ValueType, KeyType>::Leaf*
 art_tree<ValueType, KeyType>::minimum() const {
-  return root_->minimum();
+  return root_ ? root_->minimum() : nullptr;
 }
 
 /**
@@ -769,7 +769,7 @@ art_tree<ValueType, KeyType>::minimum() const {
 template <typename ValueType, typename KeyType>
 typename art_tree<ValueType, KeyType>::Leaf*
 art_tree<ValueType, KeyType>::maximum() const {
-  return root_->maximum();
+  return root_ ? root_->maximum() : nullptr;
 }
 
 template <typename ValueType, typename KeyType>
