Prevent pressing submit if the Markdown widget is empty

core/templates/core/markdown_textarea.jinja

@@ -175,24 +175,25 @@
 			let parentDiv = textarea.parentElement
 			let submitPressed = false
 
-			function checkMarkdownInput() {
+			function checkMarkdownInput(e) {
 				// an attribute is null if it does not exist, else a string
 				let required = textarea.getAttribute('required') != null
 				let length = textarea.value.trim().length
 
 				if (required && length == 0) {
 					parentDiv.style.boxShadow = 'red 0px 0px 1.5px 1px'
+					e.preventDefault()
 				} else {
 					parentDiv.style.boxShadow = ''
 				}
 			}
 
-			submit.addEventListener('click', () => {
+			submit.addEventListener('click', (e) => {
 				if (!submitPressed) {
 					easymde.codemirror.on('change', checkMarkdownInput)
 				}
 				submitPressed = true
-				checkMarkdownInput()
+				checkMarkdownInput(e)
 			})
 		})
 	</script>