This DEV-only field was added in 836331ba5f69f2cc53b273ec073fae116db14302 by @sebmarkbage but it's not being used anymore to my knowledge.
let nextChildren;
  if (
    didCaptureError &&
    typeof Component.getDerivedStateFromError !== 'function'
  ) {
    
    
    
    
    
    nextChildren = null;
    if (enableProfilerTimer) {
      stopProfilerTimerIfRunning(workInProgress);
    }
  } else {
    if (__DEV__) {
      setIsRendering(true);
      nextChildren = instance.render();
      if (
        debugRenderPhaseSideEffectsForStrictMode &&
        workInProgress.mode & StrictLegacyMode
      ) {
        disableLogs();
        try {
          instance.render();
        } finally {
          reenableLogs();
        }
      }
      setIsRendering(false);