Use Integer instead of int in KafkaClusterSpec replicas

api/src/main/java/io/strimzi/api/kafka/model/kafka/KafkaClusterSpec.java

@@ -73,7 +73,7 @@ public class KafkaClusterSpec implements HasConfigurableMetrics, HasConfigurable
     private String brokerRackInitImage;
     private Rack rack;
     private Logging logging;
-    private int replicas;
+    private Integer replicas;
     private String image;
     private ResourceRequirements resources;
     private Probe livenessProbe;
@@ -164,11 +164,11 @@ public void setLogging(Logging logging) {
     @Description("The number of pods in the cluster. " +
             "This property is required when node pools are not used.")
     @Minimum(1)
-    public int getReplicas() {
+    public Integer getReplicas() {
         return replicas;
     }
 
-    public void setReplicas(int replicas) {
+    public void setReplicas(Integer replicas) {
         this.replicas = replicas;
     }
 

cluster-operator/src/main/java/io/strimzi/operator/cluster/model/KRaftUtils.java

@@ -91,7 +91,7 @@ public static void validateKafkaCrForZooKeeper(KafkaSpec kafkaSpec, boolean node
             }
 
             if (!nodePoolsEnabled)  {
-                if (kafkaSpec.getKafka().getReplicas() == 0)   {
+                if (kafkaSpec.getKafka().getReplicas() == null || kafkaSpec.getKafka().getReplicas() == 0)   {
                     errors.add("The .spec.kafka.replicas property of the Kafka custom resource is missing. " +
                             "This property is required for a ZooKeeper-based Kafka cluster that is not using Node Pools.");
                 }
@@ -136,6 +136,7 @@ public static void kraftWarnings(Kafka kafkaCr, KafkaStatus kafkaStatus)   {
      */
     public static void nodePoolWarnings(Kafka kafkaCr, KafkaStatus kafkaStatus)   {
         if (kafkaCr.getSpec().getKafka() != null
+                && kafkaCr.getSpec().getKafka().getReplicas() != null
                 && kafkaCr.getSpec().getKafka().getReplicas() > 0) {
             kafkaStatus.addCondition(StatusUtils.buildWarningCondition("UnusedReplicasConfiguration",
                     "The .spec.kafka.replicas property in the Kafka custom resource is ignored when node pools " +

cluster-operator/src/test/resources/io/strimzi/operator/cluster/model/KafkaClusterTest.withAffinityWithoutRack-Kafka.yaml

@@ -4,6 +4,7 @@ metadata:
   name: my-cluster
 spec:
   kafka:
+    replicas: 1
     listeners:
       - name: plain
         port: 9092

cluster-operator/src/test/resources/io/strimzi/operator/cluster/model/KafkaClusterTest.withRackAndAffinity-Kafka.yaml

@@ -4,6 +4,7 @@ metadata:
   name: my-cluster
 spec:
   kafka:
+    replicas: 1
     listeners:
       - name: plain
         port: 9092

cluster-operator/src/test/resources/io/strimzi/operator/cluster/model/KafkaClusterTest.withRackAndAffinityWithMoreTerms-Kafka.yaml

@@ -4,6 +4,7 @@ metadata:
   name: my-cluster
 spec:
   kafka:
+    replicas: 1
     listeners:
       - name: plain
         port: 9092

cluster-operator/src/test/resources/io/strimzi/operator/cluster/model/KafkaClusterTest.withRackWithoutAffinity-Kafka.yaml

@@ -4,6 +4,7 @@ metadata:
   name: my-cluster
 spec:
   kafka:
+    replicas: 1
     listeners:
       - name: plain
         port: 9092

cluster-operator/src/test/resources/io/strimzi/operator/cluster/model/KafkaClusterTest.withTolerations-Kafka.yaml

@@ -4,6 +4,7 @@ metadata:
   name: my-cluster
 spec:
   kafka:
+    replicas: 1
     listeners:
       - name: plain
         port: 9092