diff --git a/src/main/java/org/levigo/jadice/server/converterclient/gui/clusterhealth/rule/AbstractNumericRule.java b/src/main/java/org/levigo/jadice/server/converterclient/gui/clusterhealth/rule/AbstractNumericRule.java
index c0cc056..73dcea7 100644
--- a/src/main/java/org/levigo/jadice/server/converterclient/gui/clusterhealth/rule/AbstractNumericRule.java
+++ b/src/main/java/org/levigo/jadice/server/converterclient/gui/clusterhealth/rule/AbstractNumericRule.java
@@ -29,6 +29,9 @@ protected AbstractNumericRule(T initalLimit, JMXFunction<T> jmxFunction) {
   }
   
   public EvaluationResult<T> evaluate(MBeanServerConnection mbsc) {
+    if (!isEnabled()) {
+      return new EvaluationResult<T>(HealthStatus.UNKNOW);
+    }
     try {
       final T currentValue = jmxFunction.evaluate(mbsc);
       if (getLimit().compareTo(currentValue) <= 0) { // i.e. getLimit() <= execTime
diff --git a/src/main/java/org/levigo/jadice/server/converterclient/gui/clusterhealth/rule/EvaluationResult.java b/src/main/java/org/levigo/jadice/server/converterclient/gui/clusterhealth/rule/EvaluationResult.java
index 0d31a4f..197e98e 100644
--- a/src/main/java/org/levigo/jadice/server/converterclient/gui/clusterhealth/rule/EvaluationResult.java
+++ b/src/main/java/org/levigo/jadice/server/converterclient/gui/clusterhealth/rule/EvaluationResult.java
@@ -1,5 +1,6 @@
 package org.levigo.jadice.server.converterclient.gui.clusterhealth.rule;
 
+import java.util.Objects;
 import java.util.Optional;
 
 import org.levigo.jadice.server.converterclient.gui.clusterhealth.HealthStatus;
@@ -13,6 +14,10 @@ public class EvaluationResult<T> {
   public final Optional<T> currentValue;
 
   public final Optional<Throwable> error;
+  
+  public EvaluationResult(HealthStatus status) {
+    this(status, Optional.empty(), Optional.empty(), Optional.empty());
+  }
 
   public EvaluationResult(HealthStatus status, T currentValue) {
     this(status, Optional.of(currentValue), Optional.empty(), Optional.empty());
@@ -27,9 +32,9 @@ public EvaluationResult(HealthStatus status, Throwable error) {
   }
 
   private EvaluationResult(HealthStatus status, Optional<T> currentValue, Optional<String> message, Optional<Throwable> error) {
-    this.status = status;
-    this.currentValue = currentValue;
-    this.message = message;
-    this.error = error;
+    this.status = Objects.requireNonNull(status, "status must not be null");
+    this.currentValue = Objects.requireNonNull(currentValue, "currentValue must not be null");
+    this.message = Objects.requireNonNull(message, "message must not be null");
+    this.error = Objects.requireNonNull(error, "error must not be null");
   }
 }
diff --git a/src/main/java/org/levigo/jadice/server/converterclient/gui/clusterhealth/rule/ServerRunningRule.java b/src/main/java/org/levigo/jadice/server/converterclient/gui/clusterhealth/rule/ServerRunningRule.java
index 5c84cad..5f13af9 100644
--- a/src/main/java/org/levigo/jadice/server/converterclient/gui/clusterhealth/rule/ServerRunningRule.java
+++ b/src/main/java/org/levigo/jadice/server/converterclient/gui/clusterhealth/rule/ServerRunningRule.java
@@ -32,6 +32,9 @@ public BooleanProperty enabledProperty() {
 
   @Override
   public EvaluationResult<Boolean> evaluate(MBeanServerConnection mbsc)  {
+    if (!isEnabled()) {
+      return new EvaluationResult<>(HealthStatus.UNKNOW);
+    }
     try {
       if (JmxHelper.isRunning(mbsc)) {
         return new EvaluationResult<Boolean>(HealthStatus.GOOD, true);