fix(utils.py): function_setup empty message fix

fixes https://github.com/BerriAI/litellm/issues/2858

litellm/tests/test_function_setup.py

@@ -0,0 +1,33 @@
+# What is this?
+## Unit tests for the 'function_setup()' function
+import sys, os
+import traceback
+from dotenv import load_dotenv
+
+load_dotenv()
+import os, io
+
+sys.path.insert(
+    0, os.path.abspath("../..")
+)  # Adds the parent directory to the, system path
+import pytest, uuid
+from litellm.utils import function_setup, Rules
+from datetime import datetime
+
+
+def test_empty_content():
+    """
+    Make a chat completions request with empty content -> expect this to work
+    """
+    rules_obj = Rules()
+
+    def completion():
+        pass
+
+    function_setup(
+        original_function=completion,
+        rules_obj=rules_obj,
+        start_time=datetime.now(),
+        messages=[],
+        litellm_call_id=str(uuid.uuid4()),
+    )