getLinkState returns nan

[borninfreedom]

I used RLlib to train a robot, and the rllib returned the error

ValueError: ('Observation ({}) outside given space ({})!', array([ 0.6244375 , -0.14342715, -0.00830715,         nan,         nan,
               nan], dtype=float32), Box(-1.0, 1.5, (6,), float32))

The nan is from the code

    def _get_observation(self):
        self.object_pos = p.getBasePositionAndOrientation(self.object_id)[0]
        self.robot_pos = p.getLinkState(self.kuka_id, self.num_joints - 1)[4]
        observation = self.object_pos + self.robot_pos
        return np.array(observation).astype(np.float32)

So why getLinkState returns nan?

[borninfreedom]

I run 10 envs parallel using rllib. But if I test the only one env not using rllib, it doesn't encounter the nan error.

[erwincoumans]

It happens when you insert nan into pybullet.

[borninfreedom]

I didn't insert nan. I just called getLinkState(), and the link was the end effector.