NPE if user settings file doesn't exist

When running

<artifact:install file="/path/to/file.jar">
<pom file="/path/to/pom.xml" />
<remoteRepository refId="repo" />
</artifact:install>

you get, if ~/.m2/settings.xml is missing,

java.lang.NullPointerException
at org.apache.maven.settings.SettingsUtils.merge(SettingsUtils.java:110)
at org.apache.maven.artifact.ant.AbstractArtifactTask.initSettings(Abstr
actArtifactTask.java:264)
at org.apache.maven.artifact.ant.AbstractArtifactTask.execute(AbstractAr
tifactTask.java:643)
at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:288)
at sun.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAcces
sorImpl.java:25)