code: def clip_grad_by_norm(self, grads, clip_norm):
      clip_norm = np.asarray(clip_norm, dtype=np.float32)
      for key, grad in iteritems(grads):
          norm = np.sqrt(np.sum(grad**2))
          grad[...] = clip_norm * grad / max(clip_norm, norm)
  
imports: from six import iteritems
  import nnabla
  import nnabla.solvers
  from nnabla.testing import assert_allclose
  import numpy
  from collections import OrderedDict
  import os
label_desc: Use image node_id 7 for calling the RefSolver obj's underlying member method code with example usage: obj.clip_grad_by_norm(grads, clip_norm) without return types