diff --git a/pom.xml b/pom.xml
index 720a8fb..131165f 100644
--- a/pom.xml
+++ b/pom.xml
@@ -61,6 +61,7 @@
           <artifactId>findbugs-maven-plugin</artifactId>
           <configuration>
             <effort>Max</effort>
+            <threshold>Low</threshold>
             <failOnError>true</failOnError>
           </configuration>
           <executions>
diff --git a/src/main/java/org/jenkinsci/lib/envinject/EnvInjectAction.java b/src/main/java/org/jenkinsci/lib/envinject/EnvInjectAction.java
index 5042557..0da511e 100644
--- a/src/main/java/org/jenkinsci/lib/envinject/EnvInjectAction.java
+++ b/src/main/java/org/jenkinsci/lib/envinject/EnvInjectAction.java
@@ -10,6 +10,7 @@
 import org.kohsuke.stapler.StaplerProxy;
 
 import java.io.File;
+import java.io.InvalidObjectException;
 import java.io.ObjectStreamException;
 import java.util.Collections;
 import java.util.HashMap;
@@ -140,7 +141,11 @@ private Object writeReplace() throws ObjectStreamException {
                 toWrite = Collections.<String, String>emptyMap();
             }
 
-            if (rootDir == null) {
+            if (build == null && rootDir == null) {
+                throw new InvalidObjectException("Cannot save the environment file. Action " + this + " has no associated run instance. Target root dir is unknown");
+            }
+
+            if (rootDir == null) { // New logic
                 dao.saveEnvironment(build.getRootDir(), Maps.transformEntries(toWrite,
                         new Maps.EntryTransformer<String, String, String>() {
                             public String transformEntry(String key, String value) {
@@ -148,10 +153,9 @@ public String transformEntry(String key, String value) {
                                         ? "********" : value;
                             }
                         }));
-                return this;
+            } else { // Fall-back to the legacy logic
+                dao.saveEnvironment(rootDir, toWrite);
             }
-
-            dao.saveEnvironment(rootDir, toWrite);
         } catch (Throwable e) {
             e.printStackTrace();
         }
diff --git a/src/main/java/org/jenkinsci/lib/envinject/EnvInjectLogger.java b/src/main/java/org/jenkinsci/lib/envinject/EnvInjectLogger.java
index ddb199f..6d55220 100644
--- a/src/main/java/org/jenkinsci/lib/envinject/EnvInjectLogger.java
+++ b/src/main/java/org/jenkinsci/lib/envinject/EnvInjectLogger.java
@@ -1,5 +1,6 @@
 package org.jenkinsci.lib.envinject;
 
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import hudson.model.TaskListener;
 
 import java.io.Serializable;
@@ -8,6 +9,7 @@
 /**
  * @author Gregory Boissinot
  */
+@SuppressFBWarnings(value = "SE_NO_SERIALVERSIONID", justification = "Legacy code")
 public class EnvInjectLogger implements Serializable {
 
     @Nonnull
diff --git a/src/main/java/org/jenkinsci/lib/envinject/service/EnvInjectSavable.java b/src/main/java/org/jenkinsci/lib/envinject/service/EnvInjectSavable.java
index 5d01e31..cdf9114 100644
--- a/src/main/java/org/jenkinsci/lib/envinject/service/EnvInjectSavable.java
+++ b/src/main/java/org/jenkinsci/lib/envinject/service/EnvInjectSavable.java
@@ -11,6 +11,8 @@
 import org.kohsuke.accmod.Restricted;
 import org.kohsuke.accmod.restrictions.NoExternalUse;
 
+import javax.annotation.Nonnull;
+
 /**
  * @author Gregory Boissinot
  * @deprecated The actual version of this API class is located in EnvInject API Plugin
@@ -53,7 +55,7 @@ public Map<String, String> getEnvironment(File envInjectBaseDir) throws EnvInjec
     }
 
     @SuppressFBWarnings(value = "DM_DEFAULT_ENCODING", justification = "Deprecated class")
-    public void saveEnvironment(File rootDir, Map<String, String> envMap) throws EnvInjectException {
+    public void saveEnvironment(@Nonnull File rootDir,@Nonnull Map<String, String> envMap) throws EnvInjectException {
         FileWriter fileWriter = null;
         try {
             File f = new File(rootDir, ENVINJECT_TXT_FILENAME);
diff --git a/src/main/java/org/jenkinsci/lib/envinject/service/EnvVarsResolver.java b/src/main/java/org/jenkinsci/lib/envinject/service/EnvVarsResolver.java
index b842dff..5a2bca7 100644
--- a/src/main/java/org/jenkinsci/lib/envinject/service/EnvVarsResolver.java
+++ b/src/main/java/org/jenkinsci/lib/envinject/service/EnvVarsResolver.java
@@ -1,5 +1,6 @@
 package org.jenkinsci.lib.envinject.service;
 
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import hudson.EnvVars;
 import hudson.FilePath;
 import hudson.Util;
@@ -29,6 +30,7 @@
  */
 @Deprecated
 @Restricted(NoExternalUse.class)
+@SuppressFBWarnings(value = "SE_NO_SERIALVERSIONID", justification = "Deprecated code")
 public class EnvVarsResolver implements Serializable {
 
     public Map<String, String> getPollingEnvVars(AbstractProject project, /*can be null*/ Node node) throws EnvInjectException {
@@ -204,11 +206,7 @@ private Map<String, String> gatherEnvVarsNode(@Nonnull AbstractProject project,
         }
 
         try {
-            Map<String, String> envVars = new EnvVars(p.act(new MasterToSlaveCallable<Map<String, String>, EnvInjectException>() {
-                public Map<String, String> call() throws EnvInjectException {
-                    return EnvVars.masterEnvVars;
-                }
-            }));
+            Map<String, String> envVars = new EnvVars(p.act(new SystemEnvVarsGetter()));
 
             envVars.put("NODE_NAME", node.getNodeName());
             envVars.put("NODE_LABELS", Util.join(node.getAssignedLabels(), " "));
@@ -226,5 +224,11 @@ public Map<String, String> call() throws EnvInjectException {
         }
     }
 
+    private static final class SystemEnvVarsGetter extends MasterToSlaveCallable<Map<String, String>, EnvInjectException> {
+        public Map<String, String> call() throws EnvInjectException {
+            return EnvVars.masterEnvVars;
+        }
+    }
+
 }