[karaf] better exception message when reporting an unknown feature from the maven plugin

git-svn-id: https://svn.apache.org/repos/asf/felix/trunk@807107 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/karaf/tooling/features-maven-plugin/src/main/java/org/apache/felix/karaf/tooling/features/AddFeaturesToRepoMojo.java b/karaf/tooling/features-maven-plugin/src/main/java/org/apache/felix/karaf/tooling/features/AddFeaturesToRepoMojo.java
index d2279b8..c049293 100644
--- a/karaf/tooling/features-maven-plugin/src/main/java/org/apache/felix/karaf/tooling/features/AddFeaturesToRepoMojo.java
+++ b/karaf/tooling/features-maven-plugin/src/main/java/org/apache/felix/karaf/tooling/features/AddFeaturesToRepoMojo.java
@@ -175,6 +175,9 @@
     private void addFeatures(List<String> features, Set<String> transitiveFeatures, Map<String, Feature> featuresMap) {
         for (String feature : features) {
             Feature f = featuresMap.get(feature);
+            if (f == null) {
+                throw new IllegalArgumentException("Unable to find the feature '" + feature + "'");
+            }
             transitiveFeatures.add(feature);
             addFeatures(f.getDependencies(), transitiveFeatures, featuresMap);
         }