React Router <Link />

gistfile1.txt

# gets error

			let listItems = course.acf.videos.map(function(video){
				return <li key={video.ID}>
					<Link 
						to="/test"
						activeClassName="active"
					>video.post_title</Link>
				</li>;
			});

			return <ul>{listItems}</ul>;
      
# no errors


			let listItems = course.acf.videos.map(function(video){
				return <li key={video.ID}>{video.post_title}</li>;
			});

			return <ul>{listItems}</ul>;
      

Error is

React.createElement: type is invalid -- expected a string (for built-in components) or a class/function (for composite components) but got: undefined. You likely forgot to export your component from the file it's defined in. Check the render method of `Course`.