Clarify returntype

Author: eps1lon

src/content/reference/react/captureOwnerStack.md

@@ -29,11 +29,11 @@ const stack = captureOwnerStack();
 Call `captureOwnerStack` to get the current Owner Stack.
 
 ```js {5,5}
-import {captureOwnerStack} from 'react';
+import * as React from 'react';
 
 function Component() {
   if (process.env.NODE_ENV !== 'production') {
-    const ownerStack = captureOwnerStack();
+    const ownerStack = React.captureOwnerStack();
     console.log(ownerStack);
   }
 }
@@ -53,11 +53,11 @@ Owner Stacks are available in
 - React's event handlers (e.g. `<button onClick={...} />`)
 - React error handlers ([React Root options](/reference/react-dom/client/createRoot#parameters) `onCaughtError`, `onRecoverableError`, and `onUncaughtError`)
 
-If no Owner Stack is available, an empty string is returned (see [Troubleshooting: The Owner Stack is empty](#the-owner-stack-is-empty-the-owner-stack-is-empty)). Outside of development builds, `null` is returned (see [Troubleshooting: The Owner Stack is `null`](#the-owner-stack-is-null-the-owner-stack-is-null)).
+If no Owner Stack is available, an empty string or `null` is returned (see [Troubleshooting: The Owner Stack is empty](#the-owner-stack-is-empty-the-owner-stack-is-empty)).
 
 #### Caveats {/*caveats*/}
 
-- Owner Stacks are only available in development. `captureOwnerStack` will always return `null` outside of development.
+- Owner Stacks are only available in development. `captureOwnerStack` will not be exported in production builds (see [`captureOwnerStack` is not available](#captureownerstack-is-not-available)).
 
 <DeepDive>
 
@@ -388,13 +388,10 @@ export default function App() {
 
 ## Troubleshooting {/*troubleshooting*/}
 
-### The Owner Stack is `null` {/*the-owner-stack-is-null*/}
-
-`captureOwnerStack` was called outside of development builds. For performance reasons, React will not keep track of Owners in production.
-
 ### The Owner Stack is empty {/*the-owner-stack-is-empty*/}
 
-The call of `captureOwnerStack` happened outside of a React controlled function e.g. in a `setTimeout` callback, after a fetch or in a custom DOM event handler. During render, Effects, React event handlers, and React error handlers (e.g. `hydrateRoot#options.onCaughtError`) Owner Stacks should be available.
+The call to `captureOwnerStack()` returned `null` or the empty string (`''`).
+Owner Stacks are not available outside of a React controlled function e.g. in a `setTimeout` callback, after a fetch or in a custom DOM event handler. During render, Effects, React event handlers, and React error handlers (e.g. `hydrateRoot#options.onCaughtError`) Owner Stacks should be available.
 
 In the example below, clicking the button will log an empty Owner Stack because `captureOwnerStack` was called during a custom DOM event handler. The Owner Stack must be captured earlier e.g. by moving the call of `captureOwnerStack` into the Effect body.
 <Sandpack>
@@ -408,7 +405,7 @@ export default function App() {
     function handleEvent() {
       // Calling it in a custom DOM event handler is too late.
       // The Owner Stack will be empty at this point.
-      console.log('Owner Stack: ', captureOwnerStack());
+      console.log('Owner Stack: ', String(captureOwnerStack()));
     }
 
     document.addEventListener('click', handleEvent);
@@ -438,4 +435,20 @@ export default function App() {
 }
 ```
 
-</Sandpack>
+</Sandpack>
+
+### `captureOwnerStack` is not available {/*captureownerstack-is-not-available*/}
+
+`captureOwnerStack` is only exported in development builds. It will be `undefined` in production builds. If `captureOwnerStack` is used in files that are bundled for production and development, you should conditionally access it from a namespace import.
+
+```js
+// Don't use named imports of `captureOwnerStack` in files that are bundled for development and production.
+import {captureOwnerStack} from 'react';
+// Use a namespace import instead and access `captureOwnerStack` conditionally.
+import * as React from 'react';
+
+if ('captureOwnerStack' in React) {
+  const ownerStack = React.captureOwnerStack();
+  console.log(ownerStack);
+}
+```