oakpal-maven-plugin NPE depToArtifact

[adamcin]

Caused by: java.lang.NullPointerException
    at java.util.concurrent.ConcurrentHashMap.get (ConcurrentHashMap.java:936)
    at org.apache.maven.artifact.handler.manager.DefaultArtifactHandlerManager.getArtifactHandler (DefaultArtifactHandlerManager.java:46)
    at org.apache.maven.artifact.factory.DefaultArtifactFactory.createArtifact (DefaultArtifactFactory.java:160)
    at org.apache.maven.artifact.factory.DefaultArtifactFactory.createDependencyArtifact (DefaultArtifactFactory.java:62)
    at org.apache.maven.repository.legacy.LegacyRepositorySystem.createDependencyArtifact (LegacyRepositorySystem.java:154)
    at net.adamcin.oakpal.maven.mojo.MojoWithRepositoryParams.depToArtifact (MojoWithRepositoryParams.java:92)
    at net.adamcin.oakpal.maven.mojo.MojoWithRepositoryParams.lambda$resolveArtifacts$6 (MojoWithRepositoryParams.java:105)

[adamcin]

this appears to be applicable when referencing a preinstall artifact that isn't identified by a dependency.