This happens when the user abandons the command without creating the project:

Caused by: java.lang.StringIndexOutOfBoundsException: String index out of range: -1
at java.lang.String.substring(String.java:1937)
at org.jboss.tools.forge.ui.console.NewProjectPostProcessor.postProcess(NewProjectPostProcessor.java:54)
at org.jboss.tools.forge.ui.console.ForgeCommandProcessor$1.run(ForgeCommandProcessor.java:53)
at org.eclipse.swt.widgets.RunnableLock.run(RunnableLock.java:35)
at org.eclipse.swt.widgets.Synchronizer.runAsyncMessages(Synchronizer.java:135)