fix(nuxt): check if default slot is provided before calling it

packages/nuxt/src/app/components/nuxt-link.ts

@@ -175,7 +175,7 @@ export function defineNuxtLink (options: NuxtLinkOptions) {
           // converts `""` to `null` to prevent the attribute from being added as empty (`rel=""`)
           : firstNonUndefined<string | null>(props.rel, options.externalRelAttribute, href ? DEFAULT_EXTERNAL_REL_ATTRIBUTE : '') || null
 
-        return h('a', { href, rel, target }, slots.default())
+        return h('a', { href, rel, target }, slots.default?.())
       }
     }
   }) as unknown as DefineComponent<NuxtLinkProps>

packages/nuxt/src/app/components/utils.ts

@@ -3,7 +3,7 @@ import type { Component } from 'vue'
 
 const Fragment = {
   setup (_props, { slots }) {
-    return () => slots.default()
+    return () => slots.default?.()
   }
 }
 

packages/nuxt/src/head/runtime/components.ts

@@ -135,7 +135,7 @@ export const Base = defineComponent({
 export const Title = defineComponent({
   name: 'Title',
   setup: setupForUseMeta((_, { slots }) => {
-    const title = slots.default()?.[0]?.children || null
+    const title = slots.default?.()?.[0]?.children || null
     if (process.dev && title && typeof title !== 'string') {
       console.error('<Title> can only take a string in its default slot.')
     }