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8 changes: 4 additions & 4 deletions bigquery/google/cloud/bigquery/_pandas_helpers.py
Original file line number Diff line number Diff line change
Expand Up @@ -198,9 +198,9 @@ def dataframe_to_bq_schema(dataframe, bq_schema):
type for some or all of the DataFrame columns.

Returns:
Sequence[google.cloud.bigquery.schema.SchemaField]:
The automatically determined schema. Returns empty tuple if the
type of any column cannot be determined.
Optional[Sequence[google.cloud.bigquery.schema.SchemaField]]:
The automatically determined schema. Returns None if the type of
any column cannot be determined.
"""
if bq_schema:
for field in bq_schema:
Expand All @@ -227,7 +227,7 @@ def dataframe_to_bq_schema(dataframe, bq_schema):
bq_type = _PANDAS_DTYPE_TO_BQ.get(dtype.name)
if not bq_type:
warnings.warn("Unable to determine type of column '{}'.".format(column))
return ()
return None
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bq_field = schema.SchemaField(column, bq_type)
bq_schema_out.append(bq_field)
return tuple(bq_schema_out)
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