From 2f9872199a404b4290d81619520f04295864b16e Mon Sep 17 00:00:00 2001
From: Andrii Grynenko <andrii@fb.com>
Date: Wed, 31 Aug 2016 14:12:57 -0700
Subject: [PATCH] Properly report observable returning nullptr

Summary: Make sure exception is propagated to caller (especially when Observer is just created).

Reviewed By: yfeldblum

Differential Revision: D3798991

fbshipit-source-id: cee8452cfd40dcfbaf0e2ae2c2ee628af0362c6e
---
 folly/experimental/observer/Observable-inl.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/folly/experimental/observer/Observable-inl.h b/folly/experimental/observer/Observable-inl.h
index 75061ac2..9bd3c83d 100644
--- a/folly/experimental/observer/Observable-inl.h
+++ b/folly/experimental/observer/Observable-inl.h
@@ -42,7 +42,9 @@ class ObserverCreator<Observable, Traits>::Context {
   void update() {
     {
       auto newValue = Traits::get(observable_);
-      DCHECK(newValue);
+      if (!newValue) {
+        throw std::logic_error("Observable returned nullptr.");
+      }
       value_.swap(newValue);
     }
 
-- 
2.34.1