Add initialization of llm parameter to None in ContextChatEngine cons…

…tructor

llama-index-core/llama_index/core/chat_engine/context.py

@@ -69,6 +69,7 @@ def from_defaults(
         prefix_messages: Optional[List[ChatMessage]] = None,
         node_postprocessors: Optional[List[BaseNodePostprocessor]] = None,
         context_template: Optional[str] = None,
+        llm: Optional[LLM] = None,
         **kwargs: Any,
     ) -> "ContextChatEngine":
         """Initialize a ContextChatEngine from default parameters."""