import pandas_gbq
import pandas as pd
import numpy as np

DESTINATION_TABLE_ID = 'INSERT_YOUR_TABLE_HERE'

schema = [
 {'name': 'Id', 'type': 'INTEGER', 'mode': 'NULLABLE'},
 {'name': 'Positions',
  'type': 'RECORD',
  'mode': 'REPEATED',
  'fields': [
   {'name': 'PositionState',
    'type': 'BYTES',  # Pick something other than STRING to make sure merge of schemas works
    'mode': 'NULLABLE'}
  ]
}
]

works_df = pd.DataFrame([{
        'Id': 123,
        'Positions': None
}])

error_df = pd.DataFrame([{
        'Id': 123,
        'Positions': np.array([{
            'PositionState': None
        }])
}])

# Works with warning
# pandas_gbq.to_gbq(works_df, destination_table=DESTINATION_TABLE_ID, table_schema=schema, if_exists='replace')

# Throws error
pandas_gbq.to_gbq(error_df, destination_table=DESTINATION_TABLE_ID, table_schema=schema, if_exists='replace')