class_docstr: Write me
      
code: def update_theta(self, theta):
      if theta is not None:
          assert (
              theta.shape == self.theta.shape
          ), "Invalid theta, shape is {0} but should be {1}".format(
              theta.shape, self.theta.shape
          )
          assert not np.isnan(
              theta
          ).any(), "Invalid theta, NaN encountered"
          assert (
              theta[self.num_weights :] >= 0.0
          ).all(), (
              "Invalid theta, standard deviations must be nonnegative"
          )
          self.theta = theta
      else:
          means = np.ones(self.num_weights) * self.init_mean
          stdevs = np.ones(self.num_weights) * self.init_stdev
          self.theta = np.hstack((means, stdevs))
  
imports: from __future__ import division
  from collections import deque
  from copy import deepcopy
  import numpy
  import keras.backend
  from keras.models import Model
  from rl.core import Agent
  from rl.util import *
label_desc: Use image node_id 9 for calling the CEMAgent obj's underlying member method code with example usage: obj.update_theta(theta) without return types