USe get for doc exists

packages/backend-core/src/cache/base/index.ts

@@ -60,7 +60,7 @@ export default class BaseCache {
    */
   async withCache(
     key: string,
-    ttl: number,
+    ttl: number | null = null,
     fetchFn: any,
     opts = { useTenancy: true }
   ) {

packages/backend-core/src/db/couch/DatabaseImpl.ts

@@ -137,7 +137,7 @@ export class DatabaseImpl implements Database {
 
   async docExists(id: string): Promise<boolean> {
     try {
-      await this.get(id)
+      await this.performCall(db => () => db.head(id))
       return true
     } catch {
       return false