def collimator(*args)
      raise ArgumentError, "Expected one or none arguments, got #{args.length}." unless [0, 1].include?(args.length)
      if args.length == 1
        return @associated_collimators[args.first && args.first.to_s]
      else
        # No argument used, therefore we return the first CollimatorSetup instance:
        return @collimators.first
      end
    end
def collimator(*args)
      raise ArgumentError, "Expected one or none arguments, got #{args.length}." unless [0, 1].include?(args.length)
      if args.length == 1
        return @associated_collimators[args.first && args.first.to_s]
      else
        # No argument used, therefore we return the first CollimatorSetup instance:
        return @collimators.first
      end
    end
Gives the CollimatorSetup instance mathcing the specified type (RT Beam
 Limiting Device Type).

 @overload collimator(type)
   @param [String] type collimator device type
   @return [CollimatorSetup, NilClass] the matched collimator setup (or nil if no collimator setup is matched)
 @overload collimator
   @return [CollimatorSetup, NilClass] the first collimator setup of this instance (or nil if no child collimator setups exists)