Index: DefaultArtifactResolver.java
===================================================================
--- DefaultArtifactResolver.java	(revision 331792)
+++ DefaultArtifactResolver.java	(working copy)
@@ -79,7 +79,7 @@
             {
                 File systemFile = artifact.getFile();
 
-                if ( !systemFile.exists() )
+                if (systemFile == null || !systemFile.exists() )
                 {
                     throw new ArtifactNotFoundException(
                         "System artifact: " + artifact + " not found in path: " + systemFile, artifact );