Loosen checks on numeric values

Closes #163 (closed)

arkindex_worker/worker/metadata.py

@@ -152,7 +152,7 @@ class MetaDataMixin(object):
                 metadata.get("name"), str
             ), "name shouldn't be null and should be of type str"
 
-            assert metadata.get("value") and isinstance(
+            assert metadata.get("value") is not None and isinstance(
                 metadata.get("value"), (str, float, int)
             ), "value shouldn't be null and should be of type (str or float or int)"