code: def previous(self) -> "ArrayEntry":
          
          try:
              newval, nbef = self.before.pop()
          except IndexError:
              raise NonexistentInstance(self.json_pointer(), "previous of first") from None
          return ArrayEntry(
              self.index - 1, nbef, self.after.cons(self.value), newval,
              self.parinst, self.schema_node, self.timestamp)
docs: Return an instance node corresponding to the previous entry.
  
          Raises:
              NonexistentInstance: If the receiver is the first entry of the
                  parent array.