class_docstr: Stacked Line graph class
docstr: Custom variable initialization
code: def __init__(self, *args, **kwargs):
      """Custom variable initialization"""
      self._previous_line = None
      super(StackedLine, self).__init__(*args, **kwargs)
  
file_path: pygal/pygal/graph/stackedline.py
imports: from pygal.adapters import none_to_zero
  from pygal.graph.line import Line
label_desc: Use image node_id 1 to create a new StackedLine object from inherited base classes: Line with example: obj = StackedLine()