disallow lint warnings on backend, fix warning

backend/package.json

@@ -12,7 +12,7 @@
     "clean": "tsc --build --clean",
     "start": "node build/src/index.js",
     "dev": "nodemon -w src --ext ts --exec ts-node src/index.ts",
-    "lint": "eslint . --ext .js,.ts",
+    "lint": "eslint --max-warnings=0 --ext .js,.ts .",
     "test": "TZ=UTC NODE_ENV=development jest --runInBand --coverage --forceExit --detectOpenHandles"
   },
   "dependencies": {

backend/src/graphql/resolver/TransactionResolver.ts

@@ -53,6 +53,7 @@ async function calculateAndAddDecayTransactions(
     transactionIndiced[transaction.id] = transaction
     involvedUserIds.push(transaction.userId)
     if (transaction.transactionTypeId === TransactionTypeId.SEND) {
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
       involvedUserIds.push(transaction.sendReceiverUserId!) // TODO ensure not null properly
     }
   })