[BugFix] Throw error only for non-empty function definitions.

Add reason for the required change.


Add comment to both locations.

tensorflow/python/framework/function_def_to_graph.py

@@ -258,13 +258,15 @@ def function_def_to_graph_def(fdef, input_shapes=None):
     for attr in op_def.attr:
       if attr.type == "func":
         fname = node_def.attr[attr.name].func.name
-        if not is_function(fname):
+        # Custom ops may contain a func attr with an empty fname.
+        if fname and not is_function(fname):
           raise ValueError(f"Function {fname} was not found. Please make sure "
                            "the FunctionDef `fdef` is correct.")
       elif attr.type == "list(func)":
         for fn in node_def.attr[attr.name].list.func:
           fname = fn.name
-          if not is_function(fname):
+          # Custom ops may contain a func attr with an empty fname.
+          if fname and not is_function(fname):
             raise ValueError(f"Function {fname} was not found. Please make "
                              "sure the FunctionDef `fdef` is correct.")