I am using llama-2 locally for a RAG

I am using llama-2 locally for a RAG pipeline using llama-cpp-python. I don't want to use the default system_prompt. How do I change it? I tried using the system_prompt argument in LlamaCPP() but it didn't work:

device = torch.device("cuda:0") if torch.cuda.is_available() else torch.device("cpu")
embed_model = HuggingFaceEmbedding(model_name="BAAI/bge-small-en-v1.5", device = device, cache_folder=models_dir)
n_gpu_layers = 0 if device == "cpu" else -1
llm = LlamaCPP(
model_url=None,
model_path=f'{models_dir}/llama-2-7b-chat.Q4_K_M.gguf',
temperature=0.1,
max_new_tokens=256,
# llama2 has a context window of 4096 tokens, but we set it lower to allow for some wiggle room
context_window=3900,
generate_kwargs={},
model_kwargs={"n_gpu_layers": n_gpu_layers, "offload_kqv": True},
# transform inputs into Llama2 format
messages_to_prompt=messages_to_prompt,
completion_to_prompt=completion_to_prompt,
verbose=False,
system_prompt = ""
)
service_context = ServiceContext.from_defaults(
llm=llm,
embed_model=embed_model
)
set_global_service_context(service_context)