Foreground detector is passing a black screen

I am currently trying to work on a Smart Traffic System where I want to first detect and track cars in a given video. After doing some research and working I used the vision.ForegroundDetector and the vision.BlobAnalysis libraries. In the given snippet I seem to be having a weird issue. After the first line the image passed in becomes a black screen. As in the image is all black. I tried multiple different methods to change it but cannot seem to find a solution. This is similar to an algorithm that MathWorks implemented themselves and I do not understand why it does not work.

Here is the snippet:

filteredFrame = step(videoObject.detector, singleFrame); <- PROBLEM LIES HERE

% Remove noise and clean the image

filteredFrame = imopen(filteredFrame, strel('rectangle', [3,3]));

filteredFrame = imclose(filteredFrame, strel('rectangle', [15, 15]));

filteredFrame = imfill(filteredFrame, 'holes');

[Madhav Thakker]

How did you create videoObject.detector? You may want to add some details about what different are you doing from the example. Did you refer https://in.mathworks.com/help/vision/examples/detecting-cars-using-gaussian-mixture-models.html example?