fix: LLMResultChunk cause concatenate str and list exception (#18852)

api/core/model_runtime/utils/helper.py

@@ -1,6 +1,8 @@
 import pydantic
 from pydantic import BaseModel
 
+from core.model_runtime.entities.message_entities import PromptMessageContentUnionTypes
+
 
 def dump_model(model: BaseModel) -> dict:
     if hasattr(pydantic, "model_dump"):
@@ -8,3 +10,18 @@ def dump_model(model: BaseModel) -> dict:
         return pydantic.model_dump(model)  # type: ignore
     else:
         return model.model_dump()
+
+
+def convert_llm_result_chunk_to_str(content: None | str | list[PromptMessageContentUnionTypes]) -> str:
+    if content is None:
+        message_text = ""
+    elif isinstance(content, str):
+        message_text = content
+    elif isinstance(content, list):
+        # Assuming the list contains PromptMessageContent objects with a "data" attribute
+        message_text = "".join(
+            item.data if hasattr(item, "data") and isinstance(item.data, str) else str(item) for item in content
+        )
+    else:
+        message_text = str(content)
+    return message_text