Ambiguous error message when SAM file contains no UMI in htseq-count-umified

[jarondl]

If one runs htseq-count-umified with umi=true, but without UMIs in the SAM file, the error message is quite unclear:

Error occured when processing SAM input (line 97460 of file SAMFILE):
Traceback (most recent call last):
  File "/illumina1/YanaiLab/new_fs/tools/bin/pijpleiding_stable", line 129, in <module>
    main(args.config_file)
  File "/illumina1/YanaiLab/new_fs/tools/bin/pijpleiding_stable", line 93, in main
    segment(**parameters)
  File "/illumina1/YanaiLab/new_fs/tools/pipeline_stable/htseq_wrapper.py", line 82, in main
    results = pool.map(run_cmd, cmds)
  File "/usr/lib/python2.7/multiprocessing/pool.py", line 250, in map
    return self.map_async(func, iterable, chunksize).get()
  File "/usr/lib/python2.7/multiprocessing/pool.py", line 554, in get
    raise self._value
AttributeError: 'NoneType' object has no attribute 'group'

That is because the relevant code block ( https://github.com/yanailab/CEL-Seq-pipeline/blob/stable/htseq_count_umified.py#L50 ) assumes a umi is always matched.

A better error message should apear.