PowerBI custom visual dataView matrix valueSource is empty

I am currently trying to port a PowerBI visual from API Version 1.0.0 to Version 1.1.0.

I am creating a Visual with a matrix as a dataView. To this point my Visual works. But when I try to check if a have a valueSource for my matrix, I get returned by calling console.error(dataView.matrix.valueSources.length = 0), that: dataView.matrix.valueSources.length = 0.

In a converter Method, I'm trying to iterate over my valueSources and for each valueSource I try call addTreeChildrenValues() and then push my columns.

public update(options: powerbi.extensibility.visual.VisualUpdateOptions) {
var dataView = this.dataView = options.dataViews[0];
var viewModel: FormattedColumnsViewModel = FormattedColumnsVisual.converter(dataView);
...
}


public static converter(dataView: DataView): FormattedColumnsViewModel {
for (var i = 0; i < dataView.matrix.valueSources.length; i++) {

FormattedColumnsVisual.addTreeChildrenValues(values, dataView.matrix.rows.root.children, i);

columns.push({    headerCaption: dataView.matrix.valueSources[i].displayName,
values: values, 
formatOption: formatOption,
showNumbers: showNumbers,
width: width,
leftMargin: leftMargin, 
usableWidth: usableWidth, 
fullRange: fullRange, 
zeroPosition: zeroPosition, 
formatter: formatter  });
}

My question is:

1. Why is valueSources of dataView.matrix empty?
2. Does it have something to do with my capabilities.json file?

Capabalities.json (part of it):

{"dataRoles":[{"name":"Category","kind":0,"displayName":"Category"},{"name":"Column","kind":1,"displayName":"Value"}],"dataViewMappings":[{"matrix":{"rows":{"select":[{"for":{"in":"Category"}}],"dataReductionAlgorithm":{"top":{}}},"values":{"for":{"in":"Column"}}}}]