#vulnerable code 
                                SortedMap<Long, Long> getOffsets(MovieFragmentBox moof, long trackId) {
        isoBufferWrapper = moof.getIsoFile().getOriginalIso();
        SortedMap<Long, Long> offsets2Sizes = new TreeMap<Long, Long>();
        List<TrackFragmentBox> traf = moof.getBoxes(TrackFragmentBox.class);
        assert traf.size() == 1 : "I cannot deal with movie fragments containing more than one track fragment";
        for (TrackFragmentBox trackFragmentBox : traf) {
            if (trackFragmentBox.getTrackFragmentHeaderBox().getTrackId() == trackId) {
                long baseDataOffset;
                if (trackFragmentBox.getTrackFragmentHeaderBox().hasBaseDataOffset()) {
                    baseDataOffset = trackFragmentBox.getTrackFragmentHeaderBox().getBaseDataOffset();
                } else {
                    baseDataOffset = moof.getOffset();
                }
                TrackRunBox trun = trackFragmentBox.getTrackRunBox();
                long sampleBaseOffset = baseDataOffset + trun.getDataOffset();
                long[] sampleOffsets = trun.getSampleOffsets();
                long[] sampleSizes = trun.getSampleSizes();
                for (int i = 0; i < sampleSizes.length; i++) {
                    offsets2Sizes.put(sampleOffsets[i] + sampleBaseOffset, sampleSizes[i]);
                }
            }
        }
        return offsets2Sizes;
    } 
                            #location 15 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                SortedMap<Long, Long> getOffsets(MovieFragmentBox moof, long trackId) {
        isoBufferWrapper = moof.getIsoFile().getOriginalIso();
        SortedMap<Long, Long> offsets2Sizes = new TreeMap<Long, Long>();
        List<TrackFragmentBox> traf = moof.getBoxes(TrackFragmentBox.class);
        for (TrackFragmentBox trackFragmentBox : traf) {
            if (trackFragmentBox.getTrackFragmentHeaderBox().getTrackId() == trackId) {
                long baseDataOffset;
                if (trackFragmentBox.getTrackFragmentHeaderBox().hasBaseDataOffset()) {
                    baseDataOffset = trackFragmentBox.getTrackFragmentHeaderBox().getBaseDataOffset();
                } else {
                    baseDataOffset = moof.getOffset();
                }

                for (TrackRunBox trun: trackFragmentBox.getBoxes(TrackRunBox.class)) {
                    long sampleBaseOffset = baseDataOffset + trun.getDataOffset();
                    long[] sampleOffsets = trun.getSampleOffsets();
                    long[] sampleSizes = trun.getSampleSizes();
                    for (int i = 0; i < sampleSizes.length; i++) {
                        offsets2Sizes.put(sampleOffsets[i] + sampleBaseOffset, sampleSizes[i]);
                    }
                }
            }
        }
        return offsets2Sizes;
    }