Something wrong with get_pings or properties

gistfile1.txt

pings = get_pings(sc, app="Firefox", channel=["nightly", "aurora", "beta"], , fraction=0.05)
props = get_pings_properties(pings, ["environment/build/xpcomabi",
                                     "environment/build/version",
                                     "environment/build/buildId",
                                     "environment/settings/update/channel",
                                     "environment/settings/e10sEnabled",
                                     "payload/info/subsessionStartDate",
                                     "payload/info/subsessionLength",
                                     "payload/keyedHistograms/SUBPROCESS_ABNORMAL_ABORT"])

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-79-e4ad2336a7cd> in <module>()
      6                                      "payload/info/subsessionStartDate",
      7                                      "payload/info/subsessionLength",
----> 8                                      "payload/keyedHistograms/SUBPROCESS_ABNORMAL_ABORT"])

/home/hadoop/anaconda/lib/python2.7/site-packages/moztelemetry/spark.pyc in get_pings_properties(pings, paths, only_median, with_processes)
    117     automatically merged with the parent histogram.
    118     """
--> 119     if type(pings.first()) == str:
    120         pings = pings.map(lambda p: json.loads(p))
    121 

/home/hadoop/spark/python/pyspark/rdd.pyc in first(self)
   1243         if rs:
   1244             return rs[0]
-> 1245         raise ValueError("RDD is empty")
   1246 
   1247     def isEmpty(self):

ValueError: RDD is empty