TCA-1052 - hide duration in course outline if this is not provided (eg. code interview)

Author: vas3a

src-ts/tools/learn/learn-lib/course-outline/collapsible-item/CollapsibleItem.tsx

@@ -147,7 +147,7 @@ const CollapsibleItem: FC<CollapsibleItemProps> = (props: CollapsibleItemProps)
                             {' '}
                             Lessons
                         </span>
-                        {props.duration && (
+                        {!!props.duration && (
                             <span className={styles['summary-item']}>
                                 <IconOutline.ClockIcon />
                                 {props.duration}