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.
code: def __init__(
      self, close: pd.Series, volume: pd.Series, fillna: bool = False
  ):
      self._close = close
      self._volume = volume
      self._fillna = fillna
      self._run()
  
imports: import typing
  import numpy
  import pandas
  from ta.utils import IndicatorMixin, _ema
label_desc: Use image node_id 1 to create a new NegativeVolumeIndexIndicator object from inherited base classes: IndicatorMixin with example: obj = NegativeVolumeIndexIndicator(close, volume, fillna)