fix(ObjectPage): prevent crash on re-mount (#1317)

Author: MarcusNotheis

packages/main/src/components/ObjectPage/ObjectPageUtils.ts

@@ -12,7 +12,7 @@ export const extractSectionIdFromHtmlId = (id: string) => {
 };
 
 export const getLastObjectPageSection = (ref: RefObject<HTMLDivElement>): HTMLElement => {
-  const sections = ref.current.querySelectorAll<HTMLElement>('[id^="ObjectPageSection"]');
+  const sections = ref.current?.querySelectorAll<HTMLElement>('[id^="ObjectPageSection"]');
   if (!sections || sections.length < 1) {
     return null;
   }

packages/main/src/components/ObjectPage/index.tsx

@@ -316,23 +316,31 @@ const ObjectPage: FC<ObjectPagePropTypes> = forwardRef((props: ObjectPagePropTyp
 
   useEffect(() => {
     const fillerDivObserver = new ResizeObserver(() => {
+      let heightDiff = 0;
+
       const maxHeight = Math.min(objectPageRef.current?.clientHeight, window.innerHeight);
       const availableScrollHeight = maxHeight - totalHeaderHeight;
       const lastSectionDomRef = getLastObjectPageSection(objectPageRef);
-      const subSections = lastSectionDomRef.querySelectorAll('[id^="ObjectPageSubSection"]');
 
-      let lastSubSectionHeight;
-      if (subSections.length > 0) {
-        lastSubSectionHeight = (subSections[subSections.length - 1] as HTMLElement).offsetHeight;
-      } else {
-        lastSubSectionHeight =
-          lastSectionDomRef.offsetHeight -
-          lastSectionDomRef.querySelector<HTMLElement>("[role='heading']").offsetHeight;
-      }
+      if (lastSectionDomRef) {
+        const subSections = lastSectionDomRef.querySelectorAll('[id^="ObjectPageSubSection"]');
+
+        let lastSubSectionHeight;
+        if (subSections.length > 0) {
+          lastSubSectionHeight = (subSections[subSections.length - 1] as HTMLElement).offsetHeight;
+        } else {
+          lastSubSectionHeight =
+            lastSectionDomRef.offsetHeight -
+            lastSectionDomRef.querySelector<HTMLElement>("[role='heading']").offsetHeight;
+        }
+
+        heightDiff = Math.max(0, availableScrollHeight - lastSubSectionHeight);
 
-      let heightDiff = availableScrollHeight - lastSubSectionHeight;
+        if (isNaN(heightDiff)) {
+          heightDiff = 0;
+        }
+      }
 
-      heightDiff = heightDiff > 0 ? heightDiff : 0;
       objectPageRef.current?.style.setProperty(ObjectPageCssVariables.lastSectionMargin, `${heightDiff}px`);
     });