fix: validation (better #8456) (#8461)

* Revert "revert 484e023c0"

This reverts commit c03b70c949.

* also allow pure renote

* fix checks for pure renote

packages/backend/src/server/api/endpoints/users/followers.ts

@@ -38,14 +38,29 @@ export const meta = {
 export const paramDef = {
 	type: 'object',
 	properties: {
-		userId: { type: 'string', format: 'misskey:id' },
-		username: { type: 'string' },
-		host: { type: 'string', nullable: true },
 		sinceId: { type: 'string', format: 'misskey:id' },
 		untilId: { type: 'string', format: 'misskey:id' },
 		limit: { type: 'integer', minimum: 1, maximum: 100, default: 10 },
 	},
-	required: [],
+	anyOf: [
+		{
+			properties: {
+				userId: { type: 'string', format: 'misskey:id' },
+			},
+			required: ['userId'],
+		},
+		{
+			properties: {
+				username: { type: 'string' },
+				host: {
+					type: 'string',
+					nullable: true,
+					description: 'The local host is represented with `null`.',
+				},
+			},
+			required: ['username', 'host'],
+		},
+	],
 } as const;
 
 // eslint-disable-next-line import/no-default-export