Deserializing JSON array of integers to List<Integer>

I've got the following code:

@ApplicationScoped
@Path("/sets")
@Consumes(MediaType.APPLICATION_JSON)
@Produces(MediaType.APPLICATION_JSON)
public class PartitionSet {
@Path("/form")
@POST
public Response create(List<List<BigDecimal>> partitions){
Map<String, Integer> obj = new HashMap<String, Integer>();
obj.put("numPartitions", partitions.size());
buildGraph(partitions);
return Response.status(Status.OK).entity(obj).build();
}

This actually works correctly, but I'd like to be able to have that argument to the "create" method be List<List<Integer>> instead of the BigDecimal that the jsonb deserializer seems to be using. Is there a way to do that?
My pom has the following dependency. Should I be using a different one to make this work?

<dependency>
<groupId>io.quarkus</groupId>
<artifactId>quarkus-resteasy-reactive-jsonb</artifactId>
</dependency>
`

If I simply change the argument to List<List<Integer>>, there is no failure in the deserialization. However, when it comes to using the result of the deserialization (when I do partitions.get(<some number>).get(<some number>)), I get:

java.lang.ClassCastException: class java.math.BigDecimal cannot be cast to class java.lang.Integer (java.math.BigDecimal and java.lang.Integer are in module java.base of loader 'bootstrap')

I'm not sure why the error message talks about which module those classes are in. Should I care?

[Edited to add]
Example of JSON provided as input:
[
[
16, 15, 2, 1
],
[
16, 14, 3, 1
]
]

I've fixed this by defining a JsonbAdapter:

public class IntegerSerializer implements JsonbAdapter<Integer, BigDecimal>{
@Override
public BigDecimal adaptToJson(Integer obj) throws Exception {
return new BigDecimal(obj);
}
@Override
public Integer adaptFromJson(BigDecimal obj) throws Exception {
return obj.intValue();
}
}

....which requires a JsonbConfigCustomizer:

@Singleton
public class IntegerSerConfig implements JsonbConfigCustomizer{
@Override
public void customize(JsonbConfig jsonbConfig) {
System.out.println("Configuring....");
jsonbConfig.withAdapters(new IntegerSerializer());
}
}

For some reason, this would not work with the jsonb reactive extensions, so in my pom, I switched to the following dependencies:

    <dependency>
<groupId>io.quarkus</groupId>
<artifactId>quarkus-resteasy</artifactId>
</dependency>
<dependency>
<groupId>io.quarkus</groupId>
<artifactId>quarkus-resteasy-jsonb</artifactId>
</dependency>