STY: Whitespace between class definitions.

IPython/utils/traitlets.py

@@ -984,18 +984,21 b' class ForwardDeclaredMixin(object):'
                 "Module {} has no attribute {}".format(modname, self.klass)
             )
 
+
 class ForwardDeclaredType(ForwardDeclaredMixin, Type):
     """
     Forward-declared version of Type.
     """
     pass
 
+
 class ForwardDeclaredInstance(ForwardDeclaredMixin, Instance):
     """
     Forward-declared version of Instance.
     """
     pass
 
+
 class This(ClassBasedTraitType):
     """A trait for instances of the class containing this trait.