INTERNALERROR> ValueError: Key backend: '' is not a valid value for backend; supported values are
['GTK3Agg', 'GTK3Cairo', 'MacOSX', 'nbAgg', 'Qt4Agg', 'Qt4Cairo', 'Qt5Agg', 'Qt5Cairo',
'TkAgg', 'TkCairo', 'WebAgg', 'WX', 'WXAgg', 'WXCairo', 'agg', 'cairo',
'pdf', 'pgf', 'ps', 'svg', 'template']

MatplotlibDeprecationWarning:
The validCap attribute was deprecated in Matplotlib 3.4 and will be removed two minor releases later.
  return getattr(obj, attr, *defargs)
MatplotlibDeprecationWarning:
The validJoin attribute was deprecated in Matplotlib 3.4 and will be removed two minor releases later.
  return getattr(obj, attr, *defargs)