Error in activations() call when running 'Image Category Classification Using Deep Learning' Example

I've been walking through the following example and I get an error in the first call to the activations() function:

Image Category Classification Using Deep Learning - MATLAB & Simulink (mathworks.com)

The error says:

"Check for missing argument or incorrect argument data type in call to function 'activations'."

If Iuse the image data set supplied in the link, the error becomes:

"Undefined function 'activations' for input arguments of type 'nnet.cnn.LayerGraph'.

Error in Untitled7 (line 71)

trainingFeatures = activations( net, augmentedTrainingSet, featureLayer, ..."

I haven't changed any of the code, except my images are rgb, which I don't think affects this function call. Which of my inputs could be incorrect? Or am I missing necessary toolbox?

[Dominik Mattioli]

I believe I've figured it out - the example says that you can use

net = resnet50( 'Weights', 'None' );

if you don't have the resnet pretrained model installed. However, I just installed the toolbox and changed the network instantiation to

net = resnet50();

and now it works. Perhaps the documentation could be edited to note this.