class_docstr: Returns a new kernel which acts like a sum/direct sum of two kernels.
  The second kernel can be a constant.
code: def forward(self, X, Z=None, diag=False):
      if isinstance(self.kern1, Kernel):
          return self.kern0(X, Z, diag=diag) + self.kern1(
              X, Z, diag=diag
          )
      else:  # constant
          return self.kern0(X, Z, diag=diag) + self.kern1
  
imports: import numbers
  from pyro.contrib.gp.parameterized import Parameterized
label_desc: Use image node_id 1 for calling the Sum obj's underlying member method code with example usage: obj.forward(X, Z, diag) and returns: unknown, unknown