diff --git a/backend/src/graphql/resolver/ContributionResolver.ts b/backend/src/graphql/resolver/ContributionResolver.ts
index 94c47d279..839b832e1 100644
--- a/backend/src/graphql/resolver/ContributionResolver.ts
+++ b/backend/src/graphql/resolver/ContributionResolver.ts
@@ -1,7 +1,6 @@
 import { IsNull, getConnection } from '@dbTools/typeorm'
 import { Contribution as DbContribution } from '@entity/Contribution'
 import { ContributionMessage } from '@entity/ContributionMessage'
-import { DltTransaction } from '@entity/DltTransaction'
 import { Transaction as DbTransaction } from '@entity/Transaction'
 import { User as DbUser } from '@entity/User'
 import { UserContact } from '@entity/UserContact'
diff --git a/backend/src/graphql/resolver/TransactionLinkResolver.ts b/backend/src/graphql/resolver/TransactionLinkResolver.ts
index 910f6a5b0..fa91e4bdd 100644
--- a/backend/src/graphql/resolver/TransactionLinkResolver.ts
+++ b/backend/src/graphql/resolver/TransactionLinkResolver.ts
@@ -3,7 +3,6 @@ import { randomBytes } from 'crypto'
 import { getConnection } from '@dbTools/typeorm'
 import { Contribution as DbContribution } from '@entity/Contribution'
 import { ContributionLink as DbContributionLink } from '@entity/ContributionLink'
-import { DltTransaction } from '@entity/DltTransaction'
 import { Transaction as DbTransaction } from '@entity/Transaction'
 import { TransactionLink as DbTransactionLink } from '@entity/TransactionLink'
 import { User as DbUser } from '@entity/User'
diff --git a/backend/src/graphql/resolver/TransactionResolver.ts b/backend/src/graphql/resolver/TransactionResolver.ts
index aa93461c0..ba5d6e155 100644
--- a/backend/src/graphql/resolver/TransactionResolver.ts
+++ b/backend/src/graphql/resolver/TransactionResolver.ts
@@ -3,7 +3,6 @@
 /* eslint-disable @typescript-eslint/no-non-null-assertion */
 
 import { getConnection, In } from '@dbTools/typeorm'
-import { DltTransaction } from '@entity/DltTransaction'
 import { Transaction as dbTransaction } from '@entity/Transaction'
 import { TransactionLink as dbTransactionLink } from '@entity/TransactionLink'
 import { User as dbUser } from '@entity/User'
diff --git a/backend/src/util/Monitor.ts b/backend/src/util/Monitor.ts
index 474eee786..3489eff4d 100644
--- a/backend/src/util/Monitor.ts
+++ b/backend/src/util/Monitor.ts
@@ -12,12 +12,18 @@ registerEnumType(MonitorNames, {
   description: 'Name of Monitor-keys', // this one is optional
 })
 
+/* @typescript-eslint/no-extraneous-class */
 export class Monitor {
   private static locks = new Map<MonitorNames, boolean>()
 
   // eslint-disable-next-line no-useless-constructor, @typescript-eslint/no-empty-function
   private constructor() {}
 
+  private _dummy = `to avoid unexpected class with only static properties`
+  public get dummy() {
+    return this._dummy
+  }
+
   public static isLocked(key: MonitorNames): boolean | undefined {
     if (this.locks.has(key)) {
       logger.debug(`Monitor isLocked key=${key} = `, this.locks.get(key))