Could not resolve all dependencies for configuration ':springloaded'. > null ext not allowed

I am trying to build and run the default lazybones-angular-grails project and when I use gradle 2.2.1 or less with grails-gradle-plugin:2.1.2 I keep getting this error on gradle run:

'*FAILURE: Build failed with an exception. What went wrong:
Could not resolve all dependencies for configuration ':springloaded'.
> null ext not allowed.'

If I try gradle dependencies I get:

FAILURE: Build failed with an exception.
  * What went wrong:
Execution failed for task ':dependencies'.
> Could not resolve all dependencies for configuration ':bootstrap'.
   > null ext not allowed

If I try either with gradle 2.3 I get this error:

FAILURE: Build failed with an exception.
  * Where:
Build file '.../build.gradle' line: 20
  * What went wrong:
A problem occurred evaluating root project 'lazybones-angular-grails'.
> Failed to apply plugin [id 'grails']
   > Could not find method create() for arguments [main] on [].

I’m not really sure where else to begin debugging this. Any suggestions? Let me know if additional logs or stack traces would help.