Error using vision.int​ernal.Casc​adeClassif​ier/load

I have the following error with my Matlab code I want to use vision.CascadeObjectDetector to detect object in image. I have created my labelsession successfully. But when Im running i have this error. I do not have open CV install. Do i need that to use the vision.CascadeObjectDetector?. Also how to set UseROI to true?

this is my error.

Error using vision.internal.CascadeClassifier/load Invalid OpenCV XML file. An error occurred while reading C:\Users\drake\OneDrive\Documents\MATLAB\diamonds.mat.

Error in vision.CascadeObjectDetector/loadXMLFromClassModel (line 455) obj.pCascadeClassifier.load(obj.getModelPath(obj.ClassificationModel));

Error in vision.CascadeObjectDetector/set.ClassificationModel (line 231) loadXMLFromClassModel(obj);

Error in matlab.system.SystemProp/parseInputs

Error in matlab.system.SystemProp/setProperties

Error in vision.CascadeObjectDetector (line 209) setProperties(obj,nargin,varargin{:},'ClassificationModel');

Error in Ass1 (line 121) detector = vision.CascadeObjectDetector('diamonds.mat');

and here is my code. load('diamonds.mat'); detector = vision.CascadeObjectDetector('diamonds.mat');

 card1 = imread('card1.bmp');
 %detect the diamonds.
 bbox = step(detector,card1);
 %insert bounding box rectangles and return the marked image
 detectedImg = insertObjectAnnotation(card1, 'rectangle', bbox, 'diamonds');

 figure;imshow(detectedImg);

Thank you for help