#vulnerable code 
                             private ParallelExecutorMapping mapStaticMethods(ClassGroup one, ClassGroup two)
	{
		StaticMethodSignatureMapper smsm = new StaticMethodSignatureMapper();
		smsm.map(one, two);
		
		List<ParallelExecutorMapping> pmes = new ArrayList<>();
		
		for (Method m : smsm.getMap().keySet())
		{
			Collection<Method> methods = smsm.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
#fixed code
                             private ParallelExecutorMapping mapStaticMethods(ClassGroup one, ClassGroup two)
	{
		StaticMethodSignatureMapper smsm = new StaticMethodSignatureMapper();
		smsm.map(one, two);
		
		List<ParallelExecutorMapping> pmes = new ArrayList<>();
		
		for (Method m : smsm.getMap().keySet())
		{
			Collection<Method> methods = smsm.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;
	}