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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_splicejunction_file(align_dir, data):
 """ locate the splice junction file from hisat2. hisat2 outputs a novel splicesites file to go along with the provided file, if available. this combines the two together and outputs a combined file of all of the known and novel splice junctions """

    samplename = dd.get_sample_name(data)
    align_dir = os.path.dirname(dd.get_work_bam(data))
    knownfile = get_known_splicesites_file(align_dir, data)
    novelfile = os.path.join(align_dir, "%s-novelsplicesites.bed" % samplename)
    bed_files = [x for x in [knownfile, novelfile] if file_exists(x)]
    splicejunction = bed.concat(bed_files)
    splicejunctionfile = os.path.join(align_dir,
                                      "%s-splicejunctions.bed" % samplename)
    if splicejunction:
        splicejunction.saveas(splicejunctionfile)
        return splicejunctionfile
    else:
        return None