diff --git a/litellm/llms/vertex_ai/vertex_gemma_models/transformation.py b/litellm/llms/vertex_ai/vertex_gemma_models/transformation.py
index b0c7c4ead04..23dbabeaac7 100644
--- a/litellm/llms/vertex_ai/vertex_gemma_models/transformation.py
+++ b/litellm/llms/vertex_ai/vertex_gemma_models/transformation.py
@@ -189,9 +189,9 @@ class VertexGemmaConfig(OpenAIGPTConfig):
         logging_obj: Any,
         optional_params: dict,
         litellm_params: dict,
-        client= Optional[Any],
-        timeout: Optional[Union[float, httpx.Timeout]],
-        encoding: Any,
+        client= Optional[Any] = None,
+        timeout: Optional[Union[float, httpx.Timeout]]= None,
+        encoding: Any= None,
     ):
         """Synchronous completion request"""
         from litellm.llms.custom_httpx.http_handler import AsyncHTTPHandler, HTTPHandler
@@ -230,14 +230,13 @@ class VertexGemmaConfig(OpenAIGPTConfig):
             http_handler = HTTPHandler(concurrent_limit=1)
         elif isinstance(client, httpx.Client):
             http_handler = HTTPHandler(client=client)
-        else:
+        elif isinstance(client, HTTPHandler):
             http_handler = client
-        response = http_handler.post(
-            url=api_base,
-            headers=headers,
-            json=request_data,
-            timeout=timeout,
-        )
+        else:
+            raise BaseLLMException(
+                status_code=400,
+                message=f"Invalid sync client type: {type(client)}. Expected HTTPHandler or httpx.Client.",
+            )
 
         if response.status_code != 200:
             raise BaseLLMException(
@@ -287,9 +286,9 @@ class VertexGemmaConfig(OpenAIGPTConfig):
         logging_obj: Any,
         optional_params: dict,
         litellm_params: dict,
-        client: Optional[Any],
-        timeout: Optional[Union[float, httpx.Timeout]],
-        encoding: Any,
+        client: Optional[Any]= None,
+        timeout: Optional[Union[float, httpx.Timeout]]= None,
+        encoding: Any= None,
     ):
         """Asynchronous completion request"""
         from litellm.llms.custom_httpx.http_handler import (
@@ -333,8 +332,13 @@ class VertexGemmaConfig(OpenAIGPTConfig):
             http_handler = get_async_httpx_client(
                 llm_provider=LlmProviders.VERTEX_AI,
             )
-        else:
+        elif isinstance(client, (httpx.AsyncClient, AsyncHTTPHandler)):
             http_handler = client
+        else:
+            raise BaseLLMException(
+                status_code=400,
+                message=f"Invalid async client type: {type(client)}. Expected AsyncHTTPHandler or httpx.AsyncClient.",
+            )
             
         response = await http_handler.post(
             url=api_base,