Use nullish coalescing operator (#11294)

packages/frontend/src/components/global/MkMisskeyFlavoredMarkdown.ts

@@ -256,7 +256,7 @@ export default function(props: {
 			case 'mention': {
 				return [h(MkMention, {
 					key: Math.random(),
-					host: (token.props.host == null && props.author && props.author.host != null ? props.author.host : token.props.host) || host,
+					host: (token.props.host == null && props.author && props.author.host != null ? props.author.host : token.props.host) ?? host,
 					username: token.props.username,
 				})];
 			}