Fixed documentation bug for projectPoints: Distortion coefficients cannot actually be NULL

modules/calib3d/include/opencv2/calib3d.hpp

@@ -444,7 +444,7 @@ vector\<Point3f\> ), where N is the number of points in the view.
 @param cameraMatrix Camera matrix \f$A = \vecthreethree{f_x}{0}{c_x}{0}{f_y}{c_y}{0}{0}{_1}\f$ .
 @param distCoeffs Input vector of distortion coefficients
 \f$(k_1, k_2, p_1, p_2[, k_3[, k_4, k_5, k_6],[s_1, s_2, s_3, s_4]])\f$ of 4, 5, 8 or 12 elements. If
-the vector is NULL/empty, the zero distortion coefficients are assumed.
+the vector is empty, the zero distortion coefficients are assumed.
 @param imagePoints Output array of image points, 2xN/Nx2 1-channel or 1xN/Nx1 2-channel, or
 vector\<Point2f\> .
 @param jacobian Optional output 2Nx(10+\<numDistCoeffs\>) jacobian matrix of derivatives of image