Fix auto_map format for AutoTokenizer in config.json

config.json

@@ -24,6 +24,9 @@
     "AutoConfig": "configuration_nicheformer.NicheformerConfig",
     "AutoModelForMaskedLM": "modeling_nicheformer.NicheformerForHuggingFace",
     "AutoModel": "modeling_nicheformer.NicheformerForHuggingFace",
-    "AutoTokenizer": "tokenization_nicheformer.NicheformerTokenizer"
+    "AutoTokenizer": [
+      "tokenization_nicheformer.NicheformerTokenizer",
+      null
+    ]
   }
 }