handled None case in find_providers

simplemind/utils.py

@@ -1,10 +1,12 @@
+from typing import Union
 from .providers import providers
 
 
-def find_provider(provider_name: str):
+def find_provider(provider_name: Union[str, None]):
     """Find a provider by name."""
-    for provider_class in providers:
-        if provider_class.__name__.lower() == provider_name.lower():
-            # Instantiate the provider
-            return provider_class()
+    if provider_name:
+        for provider_class in providers:
+            if provider_class.__name__.lower() == provider_name.lower():
+                # Instantiate the provider
+                return provider_class()
     raise ValueError(f"Provider {provider_name} not found")