Fix: input type number warning in browsers (#4772)

src/runtime/internal/dom.ts

@@ -138,7 +138,7 @@ export function get_binding_group_value(group, __value, checked) {
 }
 
 export function to_number(value) {
-	return value === '' ? undefined : +value;
+	return value === '' ? null : +value;
 }
 
 export function time_ranges_to_array(ranges) {

test/runtime/samples/binding-input-number/_config.js

@@ -35,14 +35,14 @@ export default {
 			<p>number 44</p>
 		`);
 
-		// empty string should be treated as undefined
+		// empty string should be treated as null
 		input.value = '';
 		await input.dispatchEvent(event);
 
-		assert.equal(component.count, undefined);
+		assert.equal(component.count, null);
 		assert.htmlEqual(target.innerHTML, `
 			<input type='number'>
-			<p>undefined undefined</p>
+			<p>object null</p>
 		`);
 	}
 };