validate -> _validate

IPython/utils/traitlets.py

@@ -1059,20 +1059,7 b' class Union(TraitType):'
     def validate(self, obj, value):
         for trait_type in self.trait_types:
             try:
-                if value is None and trait_type.allow_none:
-                    return value
-                if hasattr(trait_type, 'validate'):
-                    return trait_type.validate(obj, value)
-                elif hasattr(trait_type, 'is_valid_for'):
-                    valid = trait_type.is_valid_for(value)
-                    if valid:
-                        return value
-                    else:
-                        raise TraitError('invalid value for type: %r' % value)
-                elif hasattr(trait_type, 'value_for'):
-                    return trait_type.value_for(value)
-                else:
-                    return value
+                return trait_type._validate(obj, value)
             except Exception:
                 continue
         self.error(obj, value)