When winddir is range, export fails in METAR

[grmpfhmbl]

Log:

INFO:root:Connecting to http://weather.noaa.gov/pub/data/observations/metar/stations/LOWK.TXT
INFO:root:Parsing output
INFO:root:Found 1 METAR messages
INFO:root:==== DECODED DATA ====
Traceback (most recent call last):
  File "/vol1/data/builduser/.jenkins/workspace/Metar exporter - current from NOAA.gov/sos_exporter_metar.py", line 69, in <module>
    obs.wind_dir.string(),
AttributeError: 'NoneType' object has no attribute 'string'