Inconsistently in ScreenManager behavior if displayCapabilities is null

[JulianKast]

Bug Report

Currently, if RAIR.displayCapabilities == null, the SCM will create WindowCapablity that is not null but all fields inside it will be null. Previously, we used to assume that everything is enabled when displayCapabilities is null. However, after the change and because WindowCapablity is always not null, the case is not true in all places in ScreenManager.

int getNumberOfLines() {
    if (defaultMainWindowCapability == null){
        return 4;
    }
    int linesFound = 0;
    List<TextField> textFields = defaultMainWindowCapability.getTextFields();
    TextFieldName name;
    if (textFields != null && !textFields.isEmpty()) {
        for (TextField field : textFields) {
            if (field.getName() != null) {
                name = field.getName();
                if (name == TextFieldName.mainField1 || name == TextFieldName.mainField2 || name == TextFieldName.mainField3 || name == TextFieldName.mainField4) {
                    linesFound += 1;
                }
            }
        }
    }
    return linesFound;
}

Like in prev example, it's textFields are null, the function will return 0 even though it should return 4.

We have to go over all cases and clearly define what null means for capabilities. And pay special attention to NPEs.