add sanity checks

custom_generate/generate.py

@@ -203,7 +203,8 @@ def generate(model, window_length=256, num_sink_tokens=4, **kwargs):
                 or getattr(default_global_generation_config, arg) == getattr(generation_config, arg)
             )
         )
-        if arg in kwargs or has_custom_gen_config_arg:
+        kwargs_has_arg = arg in kwargs and kwargs[arg] is not None
+        if kwargs_has_arg or has_custom_gen_config_arg:
             raise ValueError(
                 f"`{arg}` is set, but it's not supported in this custom generate function. List of "
                 f"unsupported arguments: {UNSUPPORTED_GENERATION_ARGS}"