#vulnerable code 
                             public void printState (PrintStream out) {
		Alphabet a = instances.getDataAlphabet();
		out.println ("#doc pos typeindex type topic");
		for (int di = 0; di < topics.length; di++) {
			FeatureSequence fs = (FeatureSequence) instances.get(di).getData();
			for (int token = 0; token < topics[di].length; token++) {
				int type = fs.getIndexAtPosition(token);
				out.print(di); out.print(' ');
				out.print(token); out.print(' ');
				out.print(type); out.print(' ');
				out.print(a.lookupObject(type)); out.print(' ');
				out.print(topics[di][token]); out.println();
			}
		}
	} 
                            #location 11 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                             public void printState (PrintStream out) {
		Alphabet alphabet = instances.getDataAlphabet();

		out.println ("#doc pos typeindex type topic");
		for (int doc = 0; doc < topics.size(); doc++) {

			FeatureSequence tokenSequence =
				(FeatureSequence) instances.get(doc).getData();
			FeatureSequence topicSequence =
				(FeatureSequence) instances.get(doc).getData();

			for (int token = 0; token < topicSequence.getLength(); token++) {
				int type = tokenSequence.getIndexAtPosition(token);
				int topic = topicSequence.getIndexAtPosition(token);
				out.print(doc); out.print(' ');
				out.print(token); out.print(' ');
				out.print(type); out.print(' ');
				out.print(alphabet.lookupObject(type)); out.print(' ');
				out.print(topic); out.println();
			}
		}
	}