message: More precise interpolation invariant documentation text
diff: @@ -369,7 +369,7 @@ class BettiCurve2(BaseEstimator, TransformerMixin):
  Examples
  --------
  - If pd is a persistence diagram and xs is a grid such that xs[0] >= pd.min(), then the result of
  + If pd is a persistence diagram and xs is a nonempty grid of finite values such that xs[0] >= pd.min(), then the result of
  >>> bc = BettiCurve2(xs)
  >>> result = bc(pd)
  and
  