env not required during build

src/database/start.ts

@@ -9,6 +9,7 @@ const {
 } = getConfig()
 
 async function getDatabase() {
+  if (!MONGO_URL || !MONGO_DB) return undefined
   const url = `mongodb://${MONGO_USER ? `${MONGO_USER}:${MONGO_PASS ?? ''}@` : ''}${MONGO_URL}`
   const client = new MongoClient(url)
   await client.connect()

src/next-types.d.ts

@@ -1,7 +1,7 @@
 declare module 'next/config' {
   export interface ServerRuntimeConfig {
-    MONGO_URL: string
-    MONGO_DB: string
+    MONGO_URL?: string
+    MONGO_DB?: string
     MONGO_USER?: string
     MONGO_PASS?: string
   }