code: def pubdev_6534():
      df_data = [["D", "E", "NA", "NA"], ["1", "A", "NA", "NA"]]
      df = H2OFrame.from_python(
          df_data, column_types=["factor"] * 4, na_strings=["NA"]
      )
  
      assert df.type("C1") == "enum"
      assert df.type("C2") == "enum"
      assert df.type("C3") == "int"
      assert df.type("C4") == "int"
  
      # convert empty col to enum
      df["C3"] = df["C3"].asfactor()
      # convert empty cols to char
      df["C4"] = df["C4"].ascharacter()
  
      print(df)
      assert df.type("C3") == "enum"
      assert df.type("C4") == "string"
  
label_desc: Use image node_id 1 for calling a global function with example usage: pubdev_6534() without return types