_empty is u'' for UnicodeOption

tiramisu/option.py

@@ -79,6 +79,7 @@ class Option(BaseInformation):
     __slots__ = ('_name', '_requires', '_multi', '_validator', '_default_multi',
                  '_default', '_properties', '_callback', '_multitype',
                  '_master_slaves', '_consistencies', '_empty')
+    _empty = ''
 
     def __init__(self, name, doc, default=None, default_multi=None,
                  requires=None, multi=False, callback=None,
@@ -110,7 +111,6 @@ class Option(BaseInformation):
         validate_requires_arg(requires, self._name)
         self._requires = requires
         self._multi = multi
-        self._empty = ''
         self._consistencies = None
         if validator is not None:
             if type(validator) != FunctionType:
@@ -345,6 +345,7 @@ class StrOption(Option):
 class UnicodeOption(Option):
     __slots__ = ('opt_type')
     opt_type = 'unicode'
+    _empty = u''
 
     def _validate(self, value):
         return isinstance(value, unicode)