fix: Ensure a success JSONRPCResponse with a Void result gets serialized correctly

Author: fjuma

impl/src/main/java/org/wildfly/extras/a2a/server/apps/jakarta/A2AContextResolver.java

@@ -0,0 +1,32 @@
+package org.wildfly.extras.a2a.server.apps.jakarta;
+
+import jakarta.ws.rs.ext.ContextResolver;
+import jakarta.ws.rs.ext.Provider;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.module.SimpleModule;
+
+import io.a2a.spec.DeleteTaskPushNotificationConfigResponse;
+import io.a2a.spec.JSONRPCResponse;
+import io.a2a.spec.JSONRPCVoidResponseSerializer;
+
+@Provider
+public class A2AContextResolver implements ContextResolver<ObjectMapper> {
+
+    private final ObjectMapper mapper;
+
+    public A2AContextResolver() {
+        mapper = new ObjectMapper();
+        SimpleModule module = new SimpleModule();
+        module.addSerializer(new JSONRPCVoidResponseSerializer());
+        mapper.registerModule(module);
+    }
+
+    @Override
+    public ObjectMapper getContext(Class<?> type) {
+        if (JSONRPCResponse.class.isAssignableFrom(type) && type.equals(DeleteTaskPushNotificationConfigResponse.class)) {
+            return mapper;
+        }
+        return null;
+    }
+}