class_docstr: Negative Volume Index (NVI)
  
  http://stockcharts.com/school/doku.php?id=chart_school:technical_indicators:negative_volume_inde
  
  Args:
      close(pandas.Series): dataset 'Close' column.
      volume(pandas.Series): dataset 'Volume' column.
      fillna(bool): if True, fill nan values with 1000.
docstr: Negative Volume Index (NVI)
  
  Returns:
      pandas.Series: New feature generated.
docstr_tok: ["Negative","Volume","Index","(","NVI",")","Returns",":","pandas.Series",":","New","feature","generated","."]
code: def negative_volume_index(self) -> pd.Series:
      """Negative Volume Index (NVI)
  
      Returns:
          pandas.Series: New feature generated.
      """
      # IDEA: There shouldn't be any na; might be better to throw exception
      nvi = self._check_fillna(self._nvi, value=1000)
      return pd.Series(nvi, name="nvi")
  
imports: import typing
  import numpy
  import pandas
  from ta.utils import IndicatorMixin, _ema
label_desc: Use image node_id 3 for calling the NegativeVolumeIndexIndicator obj's underlying member method code with example usage: obj.negative_volume_index() and returns: pd