code: def test_fillna_period(self):
      # GH#11343
      idx = PeriodIndex(
          ["2011-01-01 09:00", NaT, "2011-01-01 11:00"], freq="h"
      )
  
      exp = PeriodIndex(
          ["2011-01-01 09:00", "2011-01-01 10:00", "2011-01-01 11:00"],
          freq="h",
      )
      result = idx.fillna(Period("2011-01-01 10:00", freq="h"))
      tm.assert_index_equal(result, exp)
  
      exp = Index(
          [
              Period("2011-01-01 09:00", freq="h"),
              "x",
              Period("2011-01-01 11:00", freq="h"),
          ],
          dtype=object,
      )
      result = idx.fillna("x")
      tm.assert_index_equal(result, exp)
  
      exp = Index(
          [
              Period("2011-01-01 09:00", freq="h"),
              Period("2011-01-01", freq="D"),
              Period("2011-01-01 11:00", freq="h"),
          ],
          dtype=object,
      )
      result = idx.fillna(Period("2011-01-01", freq="D"))
      tm.assert_index_equal(result, exp)
  
label_desc: Use image node_id 1 for calling the TestFillNA obj's underlying member method code with example usage: obj.test_fillna_period() without return types