When I try to use the deleteRemoteArtifactsByScript feature, I get a NULL pointer exception when trying to apply my changes to the config.

The JSON parser exits with NULL.

Looking at the source on GitHub I think this is because in
https://github.com/jenkinsci/artifactdeployer-plugin/blob/master/src/main/java/org/jenkinsci/plugins/artifactdeployer/ArtifactDeployerPublisher.java#L282

you are using a Name that does not exist. I guess it should be "deleteRemoteArtifactsByScript", right?