I have the following in my code:
positionsGrid.addColumn(new ComponentRenderer<>(this::taxAmount))
.setHeader("Tax")
.setAutoWidth(true)
.setFlexGrow(0)
.setFrozen(true)
.setSortable(true)
// here (in the column footer) I would like to display the sum of all amounts from the cells above
// how do I call a custom method which would return either String or Component (latter is preferred)
.setFooter(???);