code: def trim(self, lower=None, upper=None):
          
          if upper is None:
              control = self.subseqs.seqs.model.parameters.control
              if not any(control.zonetype.values == ILAKE):
                  lower = 0.
          sequencetools.StateSequence.trim(self, lower, upper)
docs: Trim negative value whenever there is no internal lake within
          the respective subbasin.
  
          >>> from hydpy.models.hland import *
          >>> parameterstep('1d')
          >>> nmbzones(2)
          >>> zonetype(FIELD, ILAKE)
          >>> states.lz(-1.0)
          >>> states.lz
          lz(-1.0)
          >>> zonetype(FIELD, FOREST)
          >>> states.lz(-1.0)
          >>> states.lz
          lz(0.0)
          >>> states.lz(1.0)
          >>> states.lz
          lz(1.0)