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

diff --git a/folly/experimental/observer/Observable-inl.h b/folly/experimental/observer/Observable-inl.h
index 75061ac27d3b970d9d169be10b1eda11612b8673..9bd3c83d8868d36a115077a4df6ed8cc00a2177a 100644 (file)
--- 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);
     }