Silence warning by always including the default prompt + ignoring it in the chat template

additional_chat_templates/sentence_transformers.jinja

@@ -1,12 +1,14 @@
 {%- set audio_count = namespace(value=0) -%}
 {%- set image_count = namespace(value=0) -%}
 {%- set video_count = namespace(value=0) -%}
-{%- for message in messages -%}
-    {%- if loop.first and message['role'] != 'system' -%}
-        <|im_start|>system
+<|im_start|>system
 You are a helpful assistant.<|im_end|>
-{% endif -%}
-    <|im_start|>{{ message['role'] }}
+{% for message in messages -%}
+    {%- if message['role'] == 'system' -%}
+        {#- skip: the fixed system prompt above was already emitted. Any input system
+            message is only present to silence Qwen2.5-Omni's default-prompt warning. -#}
+    {%- else -%}
+        <|im_start|>{{ message['role'] }}
 {% if message['content'] is string -%}
         {{- message['content'] -}}<|im_end|>
 {% else -%}
@@ -42,6 +44,7 @@ You are a helpful assistant.<|im_end|>
         {%- endif -%}
         <|im_end|>
 {% endif -%}
+    {%- endif -%}
 {%- endfor -%}
 {%- if add_generation_prompt -%}
     <|im_start|>assistant

config_sentence_transformers.json

@@ -4,8 +4,10 @@
     "sentence_transformers": "5.5.0.dev0",
     "transformers": "5.5.0.dev0"
   },
-  "default_prompt_name": null,
+  "default_prompt_name": "default",
   "model_type": "SentenceTransformer",
-  "prompts": {},
+  "prompts": {
+    "default": "You are Qwen, a virtual human developed by the Qwen Team, Alibaba Group, capable of perceiving auditory and visual inputs, as well as generating text and speech."
+  },
   "similarity_fn_name": "cosine"
 }