Can't install a plugin with a SNAPSHOT version

java.lang.NullPointerException
	at java_util_concurrent_Callable$call.call(Unknown Source)
	at org.codehaus.griffon.cli.GriffonScriptRunner$GantCustomizer.prepareTargets(GriffonScriptRunner.java:929)
	at org.codehaus.griffon.cli.GriffonScriptRunner.executeWithGantInstance(GriffonScriptRunner.java:635)
	at org.codehaus.griffon.cli.GriffonScriptRunner.executeWithGantInstanceNoException(GriffonScriptRunner.java:655)
	at org.codehaus.griffon.cli.GriffonScriptRunner.callPluginOrGriffonScript(GriffonScriptRunner.java:385)
	at org.codehaus.griffon.cli.GriffonScriptRunner.doExecuteCommand(GriffonScriptRunner.java:298)
	at org.codehaus.griffon.cli.GriffonScriptRunner.main(GriffonScriptRunner.java:143)
	at org.codehaus.griffon.cli.support.GriffonStarter.rootLoader(GriffonStarter.java:198)
	at org.codehaus.griffon.cli.support.GriffonStarter.main(GriffonStarter.java:223)
Caused by: java.lang.NullPointerException
	at org.codehaus.griffon.artifacts.ArtifactInstallEngine$_resolveDependenciesFor_closure21_closure36.doCall(ArtifactInstallEngine.groovy:432)
	at org.codehaus.griffon.artifacts.ArtifactInstallEngine$_resolveDependenciesFor_closure21.doCall(ArtifactInstallEngine.groovy:430)
	at org.codehaus.griffon.artifacts.ArtifactInstallEngine.resolveDependenciesFor(ArtifactInstallEngine.groovy:428)
	at org.codehaus.griffon.artifacts.ArtifactInstallEngine.this$2$resolveDependenciesFor(ArtifactInstallEngine.groovy)
	at org.codehaus.griffon.artifacts.ArtifactInstallEngine$this$2$resolveDependenciesFor.callCurrent(Unknown Source)
	at org.codehaus.griffon.artifacts.ArtifactInstallEngine._installPlugins(ArtifactInstallEngine.groovy:258)
	at org.codehaus.griffon.artifacts.ArtifactInstallEngine.this$2$_installPlugins(ArtifactInstallEngine.groovy)
	at org.codehaus.griffon.artifacts.ArtifactInstallEngine$this$2$_installPlugins.callCurrent(Unknown Source)
	at org.codehaus.griffon.artifacts.ArtifactInstallEngine.resolvePluginDependencies(ArtifactInstallEngine.groovy:162)
	at org.codehaus.griffon.artifacts.ArtifactInstallEngine$resolvePluginDependencies.call(Unknown Source)
	at _GriffonSettings$_run_closure1.doCall(_GriffonSettings:41)
	at java_util_concurrent_Callable$call.call(Unknown Source)
	at java_util_concurrent_Callable$call.call(Unknown Source)
	... 9 more