code: def ensure_float_vector_or_None(F, require_order = False):
      
      if F is None:
          return F
      else:
          return ensure_float_vector(F, require_order = require_order)
docs: Ensures that F is either None, or a numpy array of floats
  
      If F is already either None or a numpy array of floats, F is returned (no copied!)
      Otherwise, checks if the argument can be converted to an array of floats and does that.
  
      Parameters
      ----------
      F: float, list of float or 1D-ndarray of float
  
      Returns
      -------
      arr : ndarray(n)
          numpy array with the floats contained in the argument