Create all Variables to be returned later by get_params.
    By default this is a no-op.
    Models that need their fprop to be called for their params to be
    created can set `needs_dummy_fprop=True` in the constructor.

def make_params(self):
    """
    Create all Variables to be returned later by get_params.
    By default this is a no-op.
    Models that need their fprop to be called for their params to be
    created can set `needs_dummy_fprop=True` in the constructor.
    """

    if self.needs_dummy_fprop:
      if hasattr(self, "_dummy_input"):
        return
      self._dummy_input = self.make_input_placeholder()
      self.fprop(self._dummy_input)