Stack trace printed while running UseRecipesWithJenkinsRuleTest.

Default constructor of RobustReflectionConverter ought to use PluginManager.
java.lang.AssertionError
	at hudson.util.RobustReflectionConverter.<init>(RobustReflectionConverter.java:82)
	at hudson.util.RobustReflectionConverter.<init>(RobustReflectionConverter.java:77)
	at hudson.security.ProjectMatrixAuthorizationStrategy$ConverterImpl.<init>(ProjectMatrixAuthorizationStrategy.java:103)

core/src/main/java/hudson/util/RobustReflectionConverter.java

@@ -53,6 +53,7 @@ import java.util.Map;
 import java.util.Set;
 import static java.util.logging.Level.WARNING;
 import java.util.logging.Logger;
+import javax.annotation.Nonnull;
 
 /**
  * Custom {@link ReflectionConverter} that handle errors more gracefully.
@@ -71,10 +72,10 @@ public class RobustReflectionConverter implements Converter {
     protected final Mapper mapper;
     protected transient SerializationMethodInvoker serializationMethodInvoker;
     private transient ReflectionProvider pureJavaReflectionProvider;
-    private final XStream2.ClassOwnership classOwnership;
+    private final @Nonnull XStream2.ClassOwnership classOwnership;
 
     public RobustReflectionConverter(Mapper mapper, ReflectionProvider reflectionProvider) {
-        this(mapper, reflectionProvider, null);
+        this(mapper, reflectionProvider, new XStream2().new PluginClassOwnership());
     }
     RobustReflectionConverter(Mapper mapper, ReflectionProvider reflectionProvider, XStream2.ClassOwnership classOwnership) {
         this.mapper = mapper;
@@ -96,7 +97,7 @@ public class RobustReflectionConverter implements Converter {
         }
 
         OwnerContext oc = OwnerContext.find(context);
-        oc.startVisiting(writer, classOwnership == null ? null : classOwnership.ownerOf(original.getClass()));
+        oc.startVisiting(writer, classOwnership.ownerOf(original.getClass()));
         try {
             doMarshal(source, writer, context);
         } finally {

core/src/main/java/hudson/util/XStream2.java

@@ -41,6 +41,7 @@ import com.thoughtworks.xstream.io.HierarchicalStreamDriver;
 import com.thoughtworks.xstream.io.HierarchicalStreamReader;
 import com.thoughtworks.xstream.io.HierarchicalStreamWriter;
 import com.thoughtworks.xstream.mapper.CannotResolveClassException;
+import edu.umd.cs.findbugs.annotations.SuppressWarnings;
 import hudson.PluginManager;
 import hudson.PluginWrapper;
 import hudson.diagnosis.OldDataMonitor;
@@ -67,7 +68,7 @@ import javax.annotation.CheckForNull;
 public class XStream2 extends XStream {
     private RobustReflectionConverter reflectionConverter;
     private final ThreadLocal<Boolean> oldData = new ThreadLocal<Boolean>();
-    private final ClassOwnership classOwnership;
+    private final @CheckForNull ClassOwnership classOwnership;
     private final Map<String,Class<?>> compatibilityAliases = new ConcurrentHashMap<String, Class<?>>();
 
     /**
@@ -111,26 +112,7 @@ public class XStream2 extends XStream {
     @Override
     protected Converter createDefaultConverter() {
         // replace default reflection converter
-        reflectionConverter = new RobustReflectionConverter(getMapper(),new JVM().bestReflectionProvider(), new ClassOwnership() {
-            PluginManager pm;
-            @Override public String ownerOf(Class<?> clazz) {
-                if (classOwnership != null) {
-                    return classOwnership.ownerOf(clazz);
-                }
-                if (pm == null) {
-                    Jenkins j = Jenkins.getInstance();
-                    if (j != null) {
-                        pm = j.getPluginManager();
-                    }
-                }
-                if (pm == null) {
-                    return null;
-                }
-                // TODO: possibly recursively scan super class to discover dependencies
-                PluginWrapper p = pm.whichPlugin(clazz);
-                return p != null ? p.getShortName() + '@' + trimVersion(p.getVersion()) : null;
-            }
-        });
+        reflectionConverter = new RobustReflectionConverter(getMapper(),new JVM().bestReflectionProvider(), new PluginClassOwnership());
         return reflectionConverter;
     }
 
@@ -377,5 +359,30 @@ public class XStream2 extends XStream {
          */
         @CheckForNull String ownerOf(Class<?> clazz);
     }
+    
+    class PluginClassOwnership implements ClassOwnership {
+
+        private PluginManager pm;
+
+        @SuppressWarnings("NP_NULL_ON_SOME_PATH_FROM_RETURN_VALUE") // classOwnership checked for null so why does FB complain?
+        @Override public String ownerOf(Class<?> clazz) {
+            if (classOwnership != null) {
+                return classOwnership.ownerOf(clazz);
+            }
+            if (pm == null) {
+                Jenkins j = Jenkins.getInstance();
+                if (j != null) {
+                    pm = j.getPluginManager();
+                }
+            }
+            if (pm == null) {
+                return null;
+            }
+            // TODO: possibly recursively scan super class to discover dependencies
+            PluginWrapper p = pm.whichPlugin(clazz);
+            return p != null ? p.getShortName() + '@' + trimVersion(p.getVersion()) : null;
+        }
+
+    }
 
 }