Update packages/bigframes/bigframes/bigquery/_operations/ai.py

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: sycai

packages/bigframes/bigframes/bigquery/_operations/ai.py

@@ -1227,7 +1227,7 @@ def _to_dataframe(
     raise ValueError(f"Unsupported data type: {type(data)}")
 
 
-def _upper_optional(input: str | None) -> str | None:
-    if input is None:
+def _upper_optional(value: str | None) -> str | None:
+    if value is None:
         return None
-    return input.upper()
+    return value.upper()