Fixing empty messages bug reported by ghunkins

Author: RyanMullins

src/transformers/models/shieldgemma2/processing_shieldgemma2.py

@@ -25,6 +25,26 @@
 
 logger = logging.get_logger(__name__)
 
+DEFAULT_SHIELDGEMMA2_POLICIES: Mapping[str, str] = {
+    "dangerous": (
+        "No Dangerous Content: The image shall not contain content that"
+        " facilitates or encourages activities that could cause real-world harm"
+        " (e.g., building firearms and explosive devices, promotion of"
+        " terrorism, instructions for suicide)."
+    ),
+    "sexual": (
+        "No Sexually Explicit content: The image shall not contain content that"
+        " depicts explicit or graphic sexual acts (e.g., pornography, erotic"
+        " nudity, depictions of rape or sexual assault)."
+    ),
+    "violence": (
+        "No Violence/Gore content: The image shall not contain content that"
+        " depicts shocking, sensational, or gratuitous violence (e.g.,"
+        " excessive blood and gore, gratuitous violence against animals,"
+        " extreme injury or moment of death)."
+    ),
+}
+
 
 class ShieldGemma2ProcessorKwargs(Gemma3ProcessorKwargs, total=False):
     policies: Optional[Sequence[str]]
@@ -65,10 +85,10 @@ def __init__(
                 the base policies ShieldGemma was trained on.
         """
         super().__init__(image_processor, tokenizer, chat_template, image_seq_length, **kwargs)
-        if policy_definitions:
-            self.policy_definitions = policy_definitions
+        if policy_definitions is None:
+            self.policy_definitions = DEFAULT_SHIELDGEMMA2_POLICIES
         else:
-            self.policy_definitions = {}
+            self.policy_definitions = policy_definitions
 
     def __call__(
         self,
@@ -138,6 +158,7 @@ def __call__(
         if (policies := kwargs.get("policies")) is None:
             policies = list(policy_definitions.keys())
 
+        # TODO(ryanmullins): Support images from PIL or URLs.
         messages = []
         expanded_images = []
         for img in images: