Robot Monitor gives an error, how to set imu0_pose_covariance?

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Hi, Robot Monitor says:

imu0_pose_covariance: The covariance at position (35), which corresponds to YAW variance, was zero. This will be replaced with a small value to maintain filter stability, but should be corrected at the message origin node.

I've set this under ekf_localization tag in my controls.yaml file;

     ...
     ekf_localization:
       ...
       imu0_pose_covariance: [1e-5, 0.0, 0.0, 0.0, 0.0, 0.0,
                              0.0, 1e-5, 0.0, 0.0, 0.0, 0.0,
                              0.0, 0.0, 1e-5, 0.0, 0.0, 0.0,
                              0.0, 0.0, 0.0, 1e-5, 0.0, 0.0,
                              0.0, 0.0, 0.0, 0.0, 1e-5, 0.0,
                              0.0, 0.0, 0.0, 0.0, 0.0, 1e-5]
       ...

But still no effect. How can I set this? Or How can I correct this problem? Thanks.