Fix: DynamicClassAttribute drops explicitly provided empty docstrings

Author: srinivasreddy

Lib/types.py

@@ -210,8 +210,10 @@ def __init__(self, fget=None, fset=None, fdel=None, doc=None):
         self.fget = fget
         self.fset = fset
         self.fdel = fdel
+        if doc is None and fget is not None:
+            doc = fget.__doc__
         # next two lines make DynamicClassAttribute act the same as property
-        self.__doc__ = doc or fget.__doc__
+        self.__doc__ = doc
         self.overwrite_doc = doc is None
         # support for abstract methods
         self.__isabstractmethod__ = bool(getattr(fget, '__isabstractmethod__', False))