Relaxed type checking of none values.

common/python/nomadcore/local_backend.py

@@ -120,7 +120,7 @@ class LocalBackend(object):
         first value of MetaName in gindex in the backend"""
         dataManager = self.dataManagers[metaName]
 
-        if self.debug:
+        if self.debug and value is not None:
 
             # Check that the value is actually of scalar type
             value_type = type(value)