diff --git a/maven-core/src/main/java/org/apache/maven/plugin/DefaultPluginManager.java b/maven-core/src/main/java/org/apache/maven/plugin/DefaultPluginManager.java
index 783dd7cdc9..af9642c401 100644
--- a/maven-core/src/main/java/org/apache/maven/plugin/DefaultPluginManager.java
+++ b/maven-core/src/main/java/org/apache/maven/plugin/DefaultPluginManager.java
@@ -143,6 +143,8 @@ public class DefaultPluginManager
         // use for the mapping manager in here
         Settings settings = session.getSettings();
         List pluginGroups = settings.getPluginGroups();
+        if ( pluginMappingManager == null ) throw new NullPointerException( "pluginMappingManager was null" );
+        if ( project == null ) throw new NullPointerException( "project was null" );
         return pluginMappingManager.getByPrefix( prefix, pluginGroups, project.getPluginArtifactRepositories(),
                                                  session.getLocalRepository() );
     }