Your command seems to work for me i.e.: mvn archetype:generate -DarchetypeGroupId=org.codehaus.mojo -DarchetypeArtifactId=javascript-ria-archetype -DarchetypeCatalog=https://nexus.codehaus.org/content/repositories/snapshots/archetype-catalog.xml
A null pointer seems to be an odd exception and suggests either a configuration or an environmental issue with your Maven installation. Please report back your findings. Kind regards, Christopher
