output: #fixed code
                               private ParallelExecutorMapping mapMethods(ClassGroup one, ClassGroup two)
  	{
  		MethodSignatureMapper msm = new MethodSignatureMapper();
  		msm.map(one, two);
  
  		List<ParallelExecutorMapping> pmes = new ArrayList<>();
  
  		for (Method m : msm.getMap().keySet())
  		{
  			Collection<Method> methods = msm.getMap().get(m);
  
  			ExecutionMapper em = new ExecutionMapper(m, methods);
  
  			ParallelExecutorMapping mapping = em.run();
  			if (mapping == null)
  				continue;
  
  			mapping.map(mapping.m1, mapping.m2);
  
  			pmes.add(mapping);
  		}
  
  		ParallelExecutorMapping finalm = new ParallelExecutorMapping(one, two);
  		for (ParallelExecutorMapping pme : pmes)
  			finalm.merge(pme);
  
  		return finalm;
  	}
input: #vulnerable code 
                               private ParallelExecutorMapping mapMethods(ClassGroup one, ClassGroup two)
  	{
  		MethodSignatureMapper msm = new MethodSignatureMapper();
  		msm.map(one, two);
  
  		List<ParallelExecutorMapping> pmes = new ArrayList<>();
  
  		for (Method m : msm.getMap().keySet())
  		{
  			Collection<Method> methods = msm.getMap().get(m);
  
  			ExecutionMapper em = new ExecutionMapper(m, methods);
  
  			ParallelExecutorMapping mapping = em.run();
  			mapping.map(mapping.m1, mapping.m2);
  
  			pmes.add(mapping);
  		}
  
  		ParallelExecutorMapping finalm = new ParallelExecutorMapping(one, two);
  		for (ParallelExecutorMapping pme : pmes)
  			finalm.merge(pme);
  
  		return finalm;
  	} 
                              #location 15 
                              #vulnerability type NULL_DEREFERENCE