[BugFix] Fix server crash on empty prompt (#7746)

Signed-off-by: Max de Bayser <mbayser@br.ibm.com>

tests/entrypoints/openai/test_prompt_validation.py

@@ -0,0 +1,22 @@
+# imports for guided decoding tests
+import re
+
+import openai
+import pytest
+
+from ...utils import RemoteOpenAIServer
+
+
+@pytest.mark.asyncio
+async def test_empty_prompt():
+    model_name = "gpt2"
+    server_args = ["--enforce-eager"]
+    with RemoteOpenAIServer(model_name, server_args) as remote_server:
+        client = remote_server.get_async_client()
+
+        with pytest.raises(openai.BadRequestError,
+                           match=re.compile('.+Prompt cannot be empty.+')):
+            await client.completions.create(model=model_name,
+                                            prompt="",
+                                            max_tokens=5,
+                                            temperature=0.0)