Fix keyerror in quality lookup

Author: mfeurer

openml/datasets/dataset.py

@@ -455,13 +455,14 @@ def _data_features_supported(self):
         return True
 
 
-
 def _check_qualities(qualities):
     if qualities is not None:
         qualities_ = {}
         for xmlquality in qualities:
             name = xmlquality['oml:name']
-            if xmlquality['oml:value'] is None:
+            if 'oml:value' not in xmlquality:
+                value = float('NaN')
+            elif xmlquality['oml:value'] is None:
                 value = float('NaN')
             elif xmlquality['oml:value'] == 'null':
                 value = float('NaN')