community: fixed KeyError: 'client' (#27345)

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---------

Co-authored-by: Max Tran <maxtra@amazon.com>

libs/community/langchain_community/llms/bedrock.py

@@ -396,7 +396,7 @@ def validate_environment(cls, values: Dict) -> Dict:
         """Validate that AWS credentials to and python package exists in environment."""
 
         # Skip creating new client if passed in constructor
-        if values["client"] is not None:
+        if values.get("client") is not None:
             return values
 
         try: