Make sure that a notebook_name is provided if writing to the filesystem

IPython/nbconvert/writers/files.py

@@ -61,6 +61,10 b' class FilesWriter(WriterBase):'
             See base for more...
             """
 
+            # Verify that a notebook name is provided.
+            if notebook_name is None:
+                raise AttributeError('notebook_name')
+
             # Pull the extension and subdir from the resources dict.
             output_extension = resources['output_extension']