When I use setPrintFormatter(NumberFormat format, String missingValueIndicator) function in NumberColumn class, I get a NPE when the table is written to file. The problem is that formatter.setColumnType(this.type()); is not called in this function variant.

Fix is to change the function definition to

public void setPrintFormatter(NumberFormat format, String missingValueIndicator) {
    setPrintFormatter(new NumberColumnFormatter(format, missingValueIndicator));
}