Repository: huggingface/transformers
Pull request: Fix TypeError: 'NoneType' object is not iterable in GenerationMixin.generate

# What does this PR do?

Fix TypeError: 'NoneType' object is not iterable in `GenerationMixin.generate`
- Fix for None layer_types

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Fixes issue introduced in:
- #44950

See the corresponding downstream issue in `trl`:
- https://github.com/huggingface/trl/issues/5425

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Changed files:
filename: src/transformers/generation/utils.py
patch: @@ -1852,7 +1852,7 @@ def _prepare_cache_for_generation(
         # linear attention models always need to pass the config, otherwise it will use an Attention cache for the LinearAttention layers
         is_linear_attention = any(
             x in ("mamba", "conv", "linear_attention")
-            for x in getattr(self.config.get_text_config(decoder=True), "layer_types", [])
+            for x in (getattr(self.config.get_text_config(decoder=True), "layer_types", []) or [])
         )
         if generation_config.cache_implementation != "dynamic_full" or is_linear_attention:
             dynamic_cache_kwargs["config"] = self.config.get_text_config(decoder=True)