fix index js warning

src/documents/templates/index.html

@@ -23,8 +23,10 @@
 		<script type="text/javascript">
 			setTimeout(() => {
 				let warning = document.getElementsByClassName('warning').item(0)
-				warning.classList.remove('hide')
-				warning.classList.add('show')
+				if (warning) {
+					warning.classList.remove('hide')
+					warning.classList.add('show')
+				}
 			}, 8000)
 		</script>
 		<style type="text/css">