Testing: Modify InternalType utilities to handle None attributes

This change does not affect the current functioning of the program,
as:
- _calc_external is only used in a context where self.internal exists
  and is a string
- _calc_internal is only used in a context where self.external exists

However, this change prevents typechecking errors once type annotations
are added, because:
- in _calc_external, self.internal.split fails if self.internal is not a
  string
- in _calc_internal, return self.external causes an error if the return
  type annotation is "str", because self.external might be None

lib/rucio/common/types.py

@@ -74,18 +74,20 @@ def __hash__(self):
 
     def _calc_external(self):
         ''' Utility to convert between internal and external representations'''
-        split = self.internal.split('@', 1)
-        if len(split) == 1:  # if cannot convert, vo is '' and this is single vo
-            vo = 'def'
-            external = split[0]
-        else:
-            vo = split[1]
-            external = split[0]
-        return vo, external
+        if isinstance(self.internal, str):
+            split = self.internal.split('@', 1)
+            if len(split) == 1:  # if cannot convert, vo is '' and this is single vo
+                vo = 'def'
+                external = split[0]
+            else:
+                vo = split[1]
+                external = split[0]
+            return vo, external
+        return '', ''
 
     def _calc_internal(self):
         ''' Utility to convert between internal and external representations'''
-        if self.vo == 'def':
+        if self.vo == 'def' and self.external is not None:
             return self.external
         internal = '{}@{}'.format(self.external, self.vo)
         return internal