error whith ACF detector

Dear all,

i want to track humans in video , i trained my own detector (Detector.mat)using ACF , and i want to track the detected human using kalamn filter , when i run the code i got this error :

Expected one output from a curly brace or dot indexing expression, but there were 0 results.

Error in detect (line 30)

results(i).Boxes = bboxes;

this is the code :

 % This function is the main entrance
 
    global obj;
 vidReader = VideoReader('Berghouse Leopard Jog.mp4');

% Create video player for visualization
vidPlayer = vision.DeployableVideoPlayer;

  load('Detector.mat');
%  resizeRatio=1.5;
    global tracks;
%     obj = setupSystemObjects('trafficvideo_name.filetype');
    tracks = initializeTracks(); % Create an empty array of tracks.
    nextId = 1; % ID of the next track
    showId = 1;
    
    % Detect moving objects, and track them across video frames.
    results = struct('Boxes',[],'Scores',[]);
    i=1;
  while(hasFrame(vidReader))  
   
    % GET DATA
 frame = readFrame(vidReader);    

            % PROCESS
    [bboxes, scores] = detect(detector,frame,'Threshold',0.9);  
    
    % Select strongest detection 
    [~,idx] = max(scores);
    results(i).Boxes = bboxes;
    results(i).Scores = scores;

  

% Compute the centroids
if isempty(bboxes)
    centroids = [];
else
    centroids = [(bboxes(:, 1) + bboxes(:, 3) / 2), ...
        (bboxes(:, 2) + bboxes(:, 4) / 2)];
end


 
 
    for i = 1:length(tracks)
 
        % Predict the current location of the track.
          bbox = tracks(i).bboxes(end, :);
    
    % Predict the current location of the track.
    predictedCentroid = predict(tracks(i).kalmanFilter);
    
    % Shift the bounding box so that its center is at the predicted location.
    tracks(i).predPosition = [predictedCentroid - bbox(3:4)/2, bbox(3:4)];
    end
 
        [assignments, unassignedTracks, unassignedDetections] = ...
        detectionToTrackAssignment(centroids);
        updateAssignedTracks(assignments,centroids, bboxes);
        updateUnassignedTracks(unassignedTracks);
        deleteLostTracks();
        [nextId]=createNewTracks(centroids, unassignedDetections, bboxes,nextId);
 
    annotation = sprintf('%s , Confidence %4.2f',detector.ModelName,scores(idx));
    frame = insertObjectAnnotation(frame,'rectangle',bboxes(idx,:),annotation);
    step(vidPlayer,frame);
    i = i+1;   

     
    toc
end