Failed to notify action. Cannot invoke method containers() on null object

As I already told you, I do not have a real usage of the plugin. It came into my root build.gradle because there a plans to integrate the gradle build into Eclipse and make usage of Eclipse WTP.

Maybe the apply-plugin, where I put this plugin, should not be in the root build script. There I had:

subprojects { subProject ->
    apply from: '../libraries.gradle'
      apply plugin: 'java'
   apply plugin: 'eclipse'
  //
um Eclipse-Projekte zu generieren
      apply plugin: 'eclipse-wtp'
 (...)

Anyway, in the momemt I do not care on this plugin, so I commented it out.