diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index fa30b84e9..703a45b87 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -9,13 +9,13 @@ You could also go the [GitPod](https://gitpod.io/#https://github.com/jenkinsci/l
 If you have the proper environment, typing:
 
 ```sh
-    mvn verify
+mvn verify
 ```
 
 should create a plugin as `target/*.hpi`, which you can install in your Jenkins instance. Running
 
 ```sh
-    mvn hpi:run -Djenkins.version=2.361.1
+mvn hpi:run
 ```
 
 allows you to spin up a test Jenkins instance on [localhost] to test your
diff --git a/src/main/java/org/jenkins/plugins/lockableresources/BackwardCompatibility.java b/src/main/java/org/jenkins/plugins/lockableresources/BackwardCompatibility.java
index 3654f810d..0a6abe87f 100644
--- a/src/main/java/org/jenkins/plugins/lockableresources/BackwardCompatibility.java
+++ b/src/main/java/org/jenkins/plugins/lockableresources/BackwardCompatibility.java
@@ -33,8 +33,8 @@ private BackwardCompatibility() {}
 
   @Initializer(after = InitMilestone.JOB_LOADED)
   public static void compatibilityMigration() {
-    LOG.log(Level.FINE, "lockable-resource-plugin compatibility migration task run");
     List<LockableResource> resources = LockableResourcesManager.get().getResources();
+    LOG.log(Level.FINE, "lockable-resource-plugin compatibility migration task run for " + resources.size() + " resources");
     for (LockableResource resource : resources) {
       List<StepContext> queuedContexts = resource.getQueuedContexts();
       if (!queuedContexts.isEmpty()) {
diff --git a/src/main/java/org/jenkins/plugins/lockableresources/LockableResource.java b/src/main/java/org/jenkins/plugins/lockableresources/LockableResource.java
index cde8dbe27..5ab0a40ee 100644
--- a/src/main/java/org/jenkins/plugins/lockableresources/LockableResource.java
+++ b/src/main/java/org/jenkins/plugins/lockableresources/LockableResource.java
@@ -37,6 +37,7 @@
 import java.util.logging.Level;
 import java.util.logging.Logger;
 import jenkins.model.Jenkins;
+import org.apache.commons.lang3.StringUtils;
 import org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SecureGroovyScript;
 import org.jenkinsci.plugins.workflow.steps.StepContext;
 import org.kohsuke.accmod.Restricted;
@@ -57,7 +58,10 @@ public class LockableResource extends AbstractDescribableImpl<LockableResource>
 
   private final String name;
   private String description = "";
-  private List<String> labels = new ArrayList<>();
+  /** @deprecated use labelsAsList instead due performance.
+   */
+  @Deprecated private transient String labels = null;
+  private List<String> labelsAsList = new ArrayList<>();
   private String reservedBy = null;
   private Date reservedTimestamp = null;
   private String note = "";
@@ -125,9 +129,20 @@ protected Object readResolve() {
     if (queuedContexts == null) { // this field was added after the initial version if this class
       queuedContexts = new ArrayList<>();
     }
+    this.repairLabels();
     return this;
   }
 
+  private void repairLabels() {
+    if (this.labels == null) {
+      return;
+    }
+
+    LOGGER.fine("Repair labels for resource " + this);
+    this.setLabels(this.labels);
+    this.labels = null;
+  }
+
   /** @deprecated Replaced with LockableResourcesManager.queuedContexts (since 1.11) */
   @Deprecated
   @ExcludeFromJacocoGeneratedReport
@@ -170,20 +185,35 @@ public boolean isEphemeral() {
     return ephemeral;
   }
 
+  /** Use getLabelsAsList instead
+   * todo This function is marked as deprecated but it is still used in tests ans
+   * jelly (config) files.
+  */
+  @Deprecated
   @Exported
   public String getLabels() {
-    return String.join(" ", this.labels);
+    if (this.labelsAsList == null) {
+      return "";
+    }
+    return String.join(" ", this.labelsAsList);
   }
 
+  /** @deprecated no equivalent at the time.
+   * todo It shall be created new one function selLabelsAsList() and use that one.
+   * But it must be checked and changed all config.jelly files and
+   * this might takes more time as expected.
+   * That the reason why a deprecated function/property is still data-bound-setter
+   */
+  // @Deprecated can not be used, because of JCaC
   @DataBoundSetter
   public void setLabels(String labels) {
     // todo use label parser from Jenkins.Label to allow the same syntax
-    this.labels = new ArrayList<>();
+    this.labelsAsList = new ArrayList<>();
     for(String label : labels.split("\\s+")) {
       if (label == null || label.isEmpty()) {
         continue;
       }
-      this.labels.add(label);
+      this.labelsAsList.add(label);
     }
   }
 
@@ -193,7 +223,7 @@ public void setLabels(String labels) {
    */
   @Exported
   public List<String> getLabelsAsList() {
-    return this.labels;
+    return this.labelsAsList;
   }
 
   /**
@@ -279,6 +309,7 @@ public boolean isReserved() {
   }
 
   @Restricted(NoExternalUse.class)
+  @CheckForNull
   public static String getUserName() {
     User current = User.current();
     if (current != null) {
@@ -294,7 +325,7 @@ public static String getUserName() {
    */
   @Restricted(NoExternalUse.class) // called by jelly
   public boolean isReservedByCurrentUser() {
-    return (this.reservedBy != null && getUserName().equals(this.reservedBy));
+    return (this.reservedBy != null && StringUtils.equals(getUserName(), this.reservedBy));
   }
 
   @Exported
diff --git a/src/main/java/org/jenkins/plugins/lockableresources/actions/LockableResourcesRootAction.java b/src/main/java/org/jenkins/plugins/lockableresources/actions/LockableResourcesRootAction.java
index b5e872cb3..48f472c34 100644
--- a/src/main/java/org/jenkins/plugins/lockableresources/actions/LockableResourcesRootAction.java
+++ b/src/main/java/org/jenkins/plugins/lockableresources/actions/LockableResourcesRootAction.java
@@ -32,6 +32,8 @@
 import org.kohsuke.stapler.export.ExportedBean;
 import org.kohsuke.stapler.interceptor.RequirePOST;
 
+import edu.umd.cs.findbugs.annotations.CheckForNull;
+
 @Extension
 @ExportedBean
 public class LockableResourcesRootAction implements RootAction {
@@ -79,6 +81,7 @@ public Api getApi() {
     return new Api(this);
   }
 
+  @CheckForNull
   public String getUserName() {
     return LockableResource.getUserName();
   }
@@ -111,9 +114,9 @@ public int getFreeResourceAmount(String label) {
     return LockableResourcesManager.get().getFreeResourceAmount(label);
   }
 
-  /** 
+  /**
    * Get percentage (0-100) usage of resources assigned to given *label*
-   * 
+   *
    * Used by {@code actions/LockableResourcesRootAction/index.jelly}
    * @since 2.19
    * @param label Label to search.
@@ -146,7 +149,7 @@ public int getNumberOfAllLabels() {
 
   /**
    * Get amount of resources assigned to given *label*
-   * 
+   *
    * Used by {@code actions/LockableResourcesRootAction/index.jelly}
    * @param label Label to search.
    * @return Amount of assigned resources.