SSB-42: enforced ra_dec to be a numpy array

CAL/CalibrationCommon/lib/datacontainers/holography_measurementset.py

@@ -256,7 +256,11 @@ class HolographyMeasurementSet(object):
                                                                           rotation_matrix,
                                                                           mjd_times):
 
-        ra, dec, epoch = list(ra_dec_epoch)
+        if not isinstance(ra_dec_epoch, numpy.ndarray):
+            raise TypeError('Expected a structured numpy array for ra_dec obtained {}'.
+                            format(ra_dec_epoch))
+        ra, dec, epoch = ra_dec_epoch.tolist()
+
         astropy_times = [HolographyMeasurementSet.__mjd_to_astropy_time(mjd_time)
                          for mjd_time in mjd_times]
         n_samples = len(astropy_times)