convertPointsFromHomogeneous Error: -215:Assertion failed) npoints >= 0

I used convertPointsFromHomogeneous function to convert homogeneous coordinates(4D) to 3D.

But I get some error:

error: (-215:Assertion failed) npoints >= 0 in function 'convertPointsFromHomogeneous'

Mycode:

cv::Mat outpoints;        
cv::triangulatePoints(l_camLposcv,l_camRposcv,m_leftcampoints,m_rightcampoints,outpoints);
cout<<outpoints.size()<<endl;
cv::Mat EculidPoints;
cv::convertPointsFromHomogeneous(outpoints,EculidPoints);
cout<<EculidPoints.size()<<endl;

outpoints is 252 x 4. How I can use this interface?