Nullable Integer support in with pandas not working as expected

import typing
from typing import Dict, Iterable, List, Optional
import apache_beam as beam
from apache_beam.options.pipeline_options import PipelineOptions

class Record(typing.NamedTuple):
    port: Optional[int]
    #port: str
recFields=set([i for i in Record.__dict__.keys() if i[:1] != '_'])
beam.coders.registry.register_coder(Record,beam.coders.RowCoder)
def extractDF(tuple):
  df=tuple[1].to_pandas()
  print(type(df.port.dtype))
  return df
input_patterns = ['data/*.parquet']
#local runner
options = PipelineOptions(flags=[], type_check_additional='all')
 
def toRecords(df):
    #df["port"]=None
    return df.to_dict('records')

with beam.Pipeline(options=options) as pipeline:
      lines = (pipeline | 'Create file patterns' >> beam.Create(input_patterns)
      | 'Read Parquet files' >>  beam.io.ReadAllFromParquetBatched(columns=recFields,with_filename=True)
      | 'Extract DF' >> beam.Map(extractDF )
      | 'To dictionaries' >> beam.FlatMap(toRecords)
      |  'ToRows' >> beam.Map(lambda x: Record(**x)).with_output_types(Record)
      | "print">> beam.Map(print))