code: def validate(self):
      
      if os.path.exists('%s/gradlew' % self.path) is False:
        raise errors.InvalidProjectStructure(message='Missing gradlew project root folder')
  
      self.touch_log('validate')
docs: Validates the app project before the build.
  
      This is the first step in the build process.
  
      Needs to be implemented by the subclass.