christian-muellers-macbook-pro:camel cmueller$ cd platforms/karaf/
christian-muellers-macbook-pro:karaf cmueller$ mvn clean install -Pvalidate
...
[WARNING] Failed to validate feature camel-twitter
[WARNING] No export found to match com.google.appengine.api.urlfetch (imported by mvn:org.apache.servicemix.bundles/org.apache.servicemix.bundles.twitter4j/2.2.5_1)
[WARNING] No export found to match twitter4j.internal.http.alternative (imported by mvn:org.apache.servicemix.bundles/org.apache.servicemix.bundles.twitter4j/2.2.5_1)