fix replace

Author: jreback

pandas/core/internals.py

@@ -718,7 +718,7 @@ def replace(self, to_replace, value, inplace=False, filter=None,
 
         inplace = validate_bool_kwarg(inplace, 'inplace')
         original_to_replace = to_replace
-        mask = isnull(self.values)
+
         # try to replace, if we raise an error, convert to ObjectBlock and
         # retry
         try:
@@ -736,12 +736,8 @@ def replace(self, to_replace, value, inplace=False, filter=None,
             return blocks
         except (TypeError, ValueError):
 
-            # we can't process the value, but nothing to do
-            if not mask.any():
-                return self if inplace else self.copy()
-
             # try again with a compatible block
-            block = self.coerce_to_target_dtype(value)
+            block = self.astype(object)
             return block.replace(
                 to_replace=original_to_replace, value=value, inplace=inplace,
                 filter=filter, regex=regex, convert=convert)