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packages/react-reconciler/src/ReactFiberWorkLoop.js

@@ -1285,6 +1285,12 @@ function handleError(root, thrownValue) {
         // boundary.
         workInProgressRootExitStatus = RootFatalErrored;
         workInProgressRootFatalError = thrownValue;
+        // Set `workInProgress` to null. This represents advancing to the next
+        // sibling, or the parent if there are no siblings. But since the root
+        // has no siblings nor a parent, we set it to null. Usually this is
+        // handled by `completeUnitOfWork` or `unwindWork`, but since we're
+        // interntionally not calling those, we need set it here.
+        // TODO: Consider calling `unwindWork` to pop the contexts.
         workInProgress = null;
         return null;
       }