keyField fetching raises error

[mkcode92]

Issue description

On migrating the quick-example profile-store from 0.7.0 to 0.8.0 the keyArgument functionality is broken.
The relevant part of the schema is:

type Query {
    getUserProfile(userId: Long!): UserProfile
}

type UserProfile {
    artistCharts: NamedArtistCharts! @topic(name: "lastlisten", keyArgument: "userId")
    ...
}

type NamedArtistCharts {
    topK: [NamedArtistCount!]!
}

type NamedArtistCount {
    id: Long!
    count: Long!
    # here
    artist: Item! @topic(name: "artists", keyField: "id")
}

type Item {
    id: Long!
    name: String!
}

The following Query

# Q1
query {
 getUserProfile(userId: 21072247) {
   artistCharts {
     topK {
       artist {
        name 
}}}}}

causes the following exception in the gateway:

WARN notprivacysafe.graphql.execution.SimpleDataFetcherExceptionHandler - Exception while fetching data (/getUserProfile/artistCharts/topK[9]/artist) : class java.lang.Integer cannot be cast to class java.lang.Long (java.lang.Integer and java.lang.Long are in module java.base of loader 'bootstrap')
java.lang.ClassCastException: class java.lang.Integer cannot be cast to class java.lang.Long (java.lang.Integer and java.lang.Long are in module java.base of loader 'bootstrap')
    at org.apache.kafka.common.serialization.LongSerializer.serialize(LongSerializer.java:19)
    at com.bakdata.quick.common.api.client.routing.PartitionRouter.findHost(PartitionRouter.java:83)
    at com.bakdata.quick.common.api.client.mirror.PartitionedMirrorClient.fetchValue(PartitionedMirrorClient.java:63)
    at com.bakdata.quick.gateway.fetcher.MirrorDataFetcherClient.fetchResult(MirrorDataFetcherClient.java:44)
    at com.bakdata.quick.gateway.fetcher.KeyFieldFetcher.get(KeyFieldFetcher.java:97)
...

Expected Behavior

Q1 should return an array of objects under the topK-field. The project is set up such that each id has a record in the "artists"-topic.

Current Behavior

The gateway throws exceptions that are propagated to the query result.

Steps to Reproduce

Deploy the profile-store example using quick-0.8.0. Execute Q1.

Detailed Description

• To exclude other causes, notice that the following query works

# Q2
query {
 getUserProfile(userId: 21072247) {
   artistCharts {
     topK {
       id
}}}}

• Also, all ids obtained with Q2 are present in the artists topic, which can be verified on the mirror endpoint.
  In an earlier deployment, the error was null, but this could not be reproduced