fix: checks if element exists before reading height

Fixes an error that would sometimes get thrown if the element
we tried to read the height from was no longer in the DOM.

packages/expandable-react/src/Expander.tsx

@@ -40,10 +40,17 @@ export const Expander = React.forwardRef(function Expander<
 
     useEffect(() => {
         const observer = new ResizeObserver(function () {
-            setExpanderHeight(internalRef.current!.offsetHeight);
+            // Default to 64 if the height can not be read because that is
+            // the height of the default summary element. In a custom component
+            // this means that the focus ring might be slightly misaligned but
+            // in most cases we will be able to read the ref correctly.
+            setExpanderHeight(internalRef.current?.offsetHeight || 64);
         });
-        observer.observe(internalRef.current!);
-        return () => observer.disconnect();
+        if (internalRef.current) {
+            observer.observe(internalRef.current);
+            return () => observer.disconnect();
+        }
+        return () => {};
     }, [setExpanderHeight]);
 
     return (

packages/jokul/src/components/expander/Expander.tsx

@@ -45,10 +45,17 @@ export const Expander = React.forwardRef(function Expander<
 
     useEffect(() => {
         const observer = new ResizeObserver(function () {
-            setExpanderHeight(internalRef.current!.offsetHeight);
+            // Default to 64 if the height can not be read because that is
+            // the height of the default summary element. In a custom component
+            // this means that the focus ring might be slightly misaligned but
+            // in most cases we will be able to read the ref correctly.
+            setExpanderHeight(internalRef.current?.offsetHeight || 64);
         });
-        observer.observe(internalRef.current!);
-        return () => observer.disconnect();
+        if (internalRef.current) {
+            observer.observe(internalRef.current);
+            return () => observer.disconnect();
+        }
+        return () => {};
     }, [setExpanderHeight]);
 
     return (