Fix the error that backendconfig doesn't work when no env specified

.ci/tests/integration/cases/global-and-namespaced-config/manifests.yaml

@@ -15,6 +15,10 @@ spec:
     topics:
       - persistent://public/default/input-java-topic
     typeClassName: java.lang.String
+  pod:
+    env:
+      - name: "podenv"
+        value: "podvalue"
   output:
     topic: persistent://public/default/output-java-topic
     typeClassName: java.lang.String

.ci/tests/integration/cases/global-and-namespaced-config/mesh-config.yaml

@@ -7,6 +7,7 @@ spec:
   env:
     namespaced1: namespacedvalue1
     shared1: fromnamespace
+    podenv: backendconfigvalue
   pod:
     liveness:
       initialDelaySeconds: 30

.ci/tests/integration/cases/global-and-namespaced-config/verify.sh

@@ -48,6 +48,15 @@ if [ $? -ne 0 ]; then
   exit 1
 fi
 
+# if the function defines the same env, it will use the value from the function instead of the backend config
+verify_env_result=$(ci::verify_env "function-sample-env" podenv podenv=podvalue 2>&1)
+if [ $? -ne 0 ]; then
+  echo "$verify_env_result"
+  kubectl delete -f "${mesh_config_file}" > /dev/null 2>&1
+  kubectl delete -f "${manifests_file}" > /dev/null 2>&1 || true
+  exit 1
+fi
+
 verify_env_result=$(ci::verify_env "function-sample-env" global1 global1=globalvalue1 2>&1)
 if [ $? -ne 0 ]; then
   echo "$verify_env_result"

controllers/spec/common.go

@@ -341,10 +341,7 @@ func PatchStatefulSet(ctx context.Context, cli client.Client, namespace string,
 	}
 
 	// merge env
-	if len(envData) == 0 {
-		return globalBackendConfigVersion, namespacedBackendConfigVersion, nil
-	}
-	globalEnvs := make([]corev1.EnvVar, 0, len(envData))
+	var globalEnvs []corev1.EnvVar
 	for key, val := range envData {
 		globalEnvs = append(globalEnvs, corev1.EnvVar{
 			Name:  key,
@@ -353,7 +350,9 @@ func PatchStatefulSet(ctx context.Context, cli client.Client, namespace string,
 	}
 	for i := range statefulSet.Spec.Template.Spec.Containers {
 		container := &statefulSet.Spec.Template.Spec.Containers[i]
-		container.Env = append(container.Env, globalEnvs...)
+		if globalEnvs != nil {
+			container.Env = append(globalEnvs, container.Env...)
+		}
 
 		// configs which only work for the workload container
 		switch container.Name {