1 files changed, 5 insertions, 4 deletions
diff --git a/src/query.ts b/src/query.ts
index dffff86eb..ee1ac2603 100644
--- a/src/query.ts
+++ b/src/query.ts
@@ -658,13 +658,13 @@ export class QueryRoot {
   /**
    * Get, modify and store an element inside a transaction.
    */
-  mutate<T>(store: Store<T>, key: any, f: (v: T) => T): QueryRoot {
+  mutate<T>(store: Store<T>, key: any, f: (v: T|undefined) => T|undefined): QueryRoot {
     this.checkFinished();
     const doPut = (tx: IDBTransaction) => {
       const reqGet = tx.objectStore(store.name).get(key);
       reqGet.onsuccess = () => {
         const r = reqGet.result;
-        let m: T;
+        let m: T|undefined;
         try {
           m = f(r);
         } catch (e) {
@@ -674,8 +674,9 @@ export class QueryRoot {
           }
           throw e;
         }
-
-        tx.objectStore(store.name).put(m);
+        if (m !== undefined && m !== null) {
+          tx.objectStore(store.name).put(m);
+        }
       };
     };
     this.scheduleFinish();