code: def test_groupby_dropna_series_by(dropna, expected):
      ser = pd.Series(
          [390.0, 350.0, 30.0, 20.0],
          index=["Falcon", "Falcon", "Parrot", "Parrot"],
          name="Max Speed",
      )
  
      result = ser.groupby(
          ["a", "b", "a", np.nan], dropna=dropna
      ).mean()
      tm.assert_series_equal(result, expected)
  
imports: import numpy
  import pytest
  from pandas.compat.pyarrow import pa_version_under10p1
  from pandas.core.dtypes.missing import na_value_for_dtype
  import pandas
  import pandas._testing
  from pandas.tests.groupby import get_groupby_method_args
label_desc: Use image node_id 5 for calling a global function with example usage: test_groupby_dropna_series_by(dropna, expected) without return types