[esrftaskgraph][hasing] handle case value us a Sized empty

esrftaskgraph/esrftaskgraph/hashing.py

@@ -3,6 +3,7 @@ import hashlib
 from collections.abc import Mapping, Iterable, Set
 import numpy
 from esrftaskgraph.utils import qualname
+from collections import Sized
 
 
 def uhashtype(_type):
@@ -10,7 +11,7 @@ def uhashtype(_type):
 
 
 def uhash(value, _hash=None):
-    """Universial hash (as opposed to python's hash).
+    """Universal hash (as opposed to python's hash).
     This is an example. Must find something better.
 
     :param value:
@@ -22,7 +23,7 @@ def uhash(value, _hash=None):
     if bdigest:
         _hash = hashlib.sha256()
     _hash.update(uhashtype(type(value)))
-    if value is None:
+    if value is None or isinstance(value, Sized) and len(value) == 0:
         pass
     elif isinstance(value, UniversalHashable):
         _hash.update(repr(value.uhash).encode())