#vulnerable code 
                             public List<Object[]> getTransformerSteps(){
		List<Object[]> steps = getSteps();

		if(steps.size() < 1){
			throw new IllegalArgumentException("Missing estimator step");
		}

		return steps.subList(0, steps.size() - 1);
	} 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                             public List<Object[]> getTransformerSteps(){
		List<Object[]> steps = getSteps();

		if(steps == null || steps.size() < 1){
			throw new IllegalArgumentException("Missing estimator step");
		}

		return steps.subList(0, steps.size() - 1);
	}