code: def test_first_valid_index(self):
      # Empty Series
      pser = pd.Series([])
      psser = ps.from_pandas(pser)
      self.assert_eq(
          pser.first_valid_index(), psser.first_valid_index()
      )
  
imports: import unittest
  import numpy
  import pandas
  from pyspark import pandas
  from pyspark.testing.pandasutils import ComparisonTestBase
  from pyspark.testing.sqlutils import SQLTestUtils
label_desc: Use image node_id 15 for calling the SeriesIndexMixin obj's underlying member method code with example usage: obj.test_first_valid_index() without return types