Repository: huggingface/transformers
Pull request: Avoid mutating user-provided arguments in preprocessing utils

# What does this PR do?

As per title, `_merge_kwargs` removes user-provided arguments via `pop` which is fixed by copying the arguments before attempting to modify them. This happens for instance when calling the `Gemma3nProcessor` with modality-specific kwargs.

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Changed files:
filename: src/transformers/processing_utils.py
patch: @@ -1226,6 +1226,9 @@ class MyProcessingKwargs(ProcessingKwargs, CommonKwargs, TextKwargs, ImagesKwarg
                 Dictionary of per-modality kwargs to be passed to each modality-specific processor.
 
         """
+        # holding a copy to avoid mutating user-provided arguments
+        kwargs = kwargs.copy()
+
         # Initialize dictionaries
         output_kwargs = {
             "text_kwargs": {},