cam_id or solvePnPRansac issue

[neeek2303]

Hello, I caught this problem:

In demo.py if I use HeadPoseEstimator() instead of estimateHeadPose() this error occures:

--> 29     hr, ht, o_l, o_r, _ = head_pose_estimator(image, landmarks, camera_matrix[cam_id])
     30     ## the easy way to get head pose information, fast and simple
     31 #     facePts = face_model.reshape(6, 1, 3)

NameError: name 'cam_id' is not defined

If I replace camera_matrix[cam_id] with camera_matrix this problem occures:

---------------------------------------------------------------------------
error                                     Traceback (most recent call last)
<ipython-input-13-a4e70c1ea3f5> in <module>
     27     landmarks = landmarks.reshape(-1, 2)
     28     head_pose_estimator = HeadPoseEstimator()
---> 29     hr, ht, o_l, o_r, _ = head_pose_estimator(image, landmarks, camera_matrix)
     30     ## the easy way to get head pose information, fast and simple
     31 #     facePts = face_model.reshape(6, 1, 3)

~/ETH-XGaze/head_pose.py in __call__(self, frame, landmarks, intrinsics, target_io_dist, visualize)
    136         # Do PnP-based head pose fitting
    137         rvec, tvec, reprojected_points, o_l, o_r, face_model = \
--> 138             self.head_pose_fit(landmarks, eos_mesh, intrinsics, scaling_factor)
    139         o_r_2D = cv.projectPoints(o_r, rvec, tvec, intrinsics, None)[0].reshape(2)
    140         o_l_2D = cv.projectPoints(o_l, rvec, tvec, intrinsics, None)[0].reshape(2)

~/ETH-XGaze/head_pose.py in head_pose_fit(self, landmarks_2D, deformed_mesh, intrinsics, scaling_factor)
     95         # Initial fit
     96         camera_matrix = intrinsics
---> 97         success, rvec, tvec, inliers = cv.solvePnPRansac(
     98             sfm_points_ibug_subset, landmarks_2D, camera_matrix, None,
     99             flags=cv.SOLVEPNP_EPNP)

error: OpenCV(4.5.2) /tmp/pip-req-build-dccdjyga/opencv/modules/calib3d/src/solvepnp.cpp:241: error: (-215:Assertion failed) npoints >= 4 && npoints == std::max(ipoints.checkVector(2, CV_32F), ipoints.checkVector(2, CV_64F)) in function 'solvePnPRansac'

could you please help?