I dont' remember what.

common/python/nomadcore/local_backend.py

@@ -7,7 +7,8 @@ logger = logging.getLogger(__name__)
 
 #===============================================================================
 class LocalBackend(object):
-    """A backend that outputs results into a regular python dictionary.
+    """A backend that outputs results into a regular python dictionary. This is
+    useful if you wan't to run the parser with python only.
     """
     def __init__(self, metaInfoEnv, fileOut=StringIO.StringIO(), debug=True):
         self.__metaInfoEnv = metaInfoEnv
@@ -218,6 +219,8 @@ class Results(object):
                         result.append(data_list)
             if len(result) == 1:
                 return result[0]
+            elif len(result) == 0:
+                raise LookupError("Could not find a parsing result for '{}'. The parser did not output this value.".format(metaname))
             else:
                 return np.array(result)