Minor fix using the corrent executor.

src/main/java/org/openhab/binding/openlicht/handler/AbstractSmartWatchHandler.java

@@ -18,7 +18,6 @@ import java.nio.ByteBuffer;
 import java.nio.DoubleBuffer;
 import java.util.HashSet;
 import java.util.Set;
-import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.TimeUnit;
 
 import org.eclipse.smarthome.core.library.types.DecimalType;
@@ -41,8 +40,6 @@ public abstract class AbstractSmartWatchHandler extends AbstractMqttHandler {
 
     private static Set<String> seenUnsupportedCategories;
 
-    private static ScheduledExecutorService executor;
-
     public AbstractSmartWatchHandler(Thing thing, ConfigurationHolder configurationHolder) {
         super(thing, configurationHolder);
         maybeSetupStatics();
@@ -55,7 +52,11 @@ public abstract class AbstractSmartWatchHandler extends AbstractMqttHandler {
                     seenUnsupportedCategories.clear();
                 }
             };
+            if (executor != null) {
                 executor.scheduleAtFixedRate(command, 0, timeout, TimeUnit.SECONDS);
+            } else {
+                logger.warn("Did not schedule reset thread for unsupported categories.");
+            }
         }
     }